GB2428286A

GB2428286A - Instantaneous water heater inlet control

Info

Publication number: GB2428286A
Application number: GB0619368A
Authority: GB
Inventors: Andrew Boulton Renfrew
Original assignee: Kohler Mira Ltd
Current assignee: Kohler Mira Ltd
Priority date: 2003-07-17
Filing date: 2004-07-16
Publication date: 2007-01-24
Anticipated expiration: 2024-07-16
Also published as: GB2428286B; GB0619368D0

Abstract

An instantaneous water heater 351 includes a heater tank 352 with a water inlet 353 connected to an incoming cold water supply via a flow control valve 356 for adjusting the water flow rate through the heater tank to provide a desired outlet water temperature from the heater tank according to user selection of any selected one of a range of outlet water temperatures. A control valve 361 responsive to the outlet water 355 temperature is operable to provide an additional separate input 354 of cold water to the heater tank 352 if the outlet water temperature exceeds a pre-determined safe limit.

Description

Water Heaters This invention relates to water heaters and in particular

instantaneous water heaters of the kind in which water is heated as it flows through a heater tank to provide a source of hot water on demand. Instantaneous water heaters are widely used to provide hot water in a variety of installations such as showers and hand washers.

Typically, the heater tank is provided with one or more electrical heating elements over which the water flows and the temperature of the water emitted from the heater tank is user controlled by varying the rate of flow of water through the heater tank. For a given flow rate and power input, the temperature of the water is raised by a fixed amount and the output water temperature can be affected by variations in water pressure, mains voltage and inlet water temperature.

Water pressure variations, which affect the rate of flow and hence temperature are usually compensated for by a flow regulating valve. A common type of flow regulating valve employs an 0-ring operable in response to the water pressure to adjust the size of flow passages to control the flow rate. More sophisticated systems make use of an output water temperature sensor with electronic feedback and control to adjust the flow regulating valve to control the flow rate.

Mains voltage variations, which affect the power input and hence temperature, and inlet water temperature variations, which affect the outlet water temperature, are less easily catered for and are typically only provided in the mOre sophisticated systems employing electronic feedback and control which adds to the cost.

Attempts have been made to provide thermostatic control of the temperature of the output water without electronic feedback and control by mixing a fixed flow of hot water from the heater tank with a separate flow of cold water via a mixing valve actuated by a wax element responsive to the output water temperature to adjust the mixing valve to maintain the selected output water temperature substantially constant.

The problem with this non electronic type of thermostatically controlled instantaneous electric water heater is that the fixed flow of hot water from the heater tank has to be fixed low enough to allow the water heater to give sufficiently hot water when the inlet water temperature is very cold during the winter months. Conversely, during the summer months when the inlet water temperature is much higher, the fixed flow of water from the heater tank is very hot and this has the undesired effect of depositing more lime scale on the heater elements than would occur in a normal water heater.

Another problem with this type of water heater is that it also has the effect of producing scalding shots of hot water when the control knob of the output mixer valve is rapidly operated, for example to increase the output water temperature from 25C to 40C.

The present invention has been made from a consideration of the foregoing problems and disadvantages of existing instantaneous water heaters.

Thus it is an object of the present invention to provide an instantaneous water heater capable of compensating for variations in one or more of the water pressure, power input and inlet water temperature in a reliable manner.

According to a first aspect of the present invention, there is provided an instantaneous water heater comprising a water heater tank, first means for supplying cold water to the heater tank, and second means for supplying cold water to the heater tank, the first means providing a substantially constant flow rate and the second means providing a variable flow rate additional to the flow rate of the first means in response to the outlet water temperature from the heater tank.

By this invention, the first means inputs cold water with a constant flow rate to the heater tank and the second means inputs additional cold water with a variable flow rate to the heater tank to adjust the total flow of cold water supplied to the heater tank to control the outlet water temperature.

In one arrangement, the first means is a cold water by-pass that provides a fixed flow of cold water and the second means is an inlet control valve that is adjustable in response to the outlet water temperature to provide a variable additional flow of cold water in accordance with user selection of a desired outlet water temperature.

Preferably, the inlet control valve controls the additional flow of cold water into the heater tank by sensing the output temperature via an actuator which directly acts on the valve to control the additional input flow.

In this way, the inlet control valve controls its own input flow dependent on the output temperature from the heater tank. As a result, the temperature within the heater tank remains predominantly the same as the user selected output temperature no matter what the temperature of the input water may be.

Preferably, the actuator comprises a memory alloy having elastic properties responsive to the outlet water temperature and the flow control valve is operable in response to an applied force by the actuator to control the additional input flow. More especially, the memory alloy actuator preferably has a modulus that changes with temperature, and more preferably has a modulus that increases with increase in temperature, to vary an actuating force applied to the flow control valve. Suitable memory alloys include nickel/titanium alloys.

In one embodiment, the flow control valve is biased towards a closed position by a biasing element that is opposed by the actuating force applied by the memory ahoy actuator. In this way, the control valve adopts an equilibrium position where the biasing element and opposing memory ahoy actuator coil are compressed by an amount according to the stiffness of the biasing element and the memory alloy actuator. The stiffness of the memory alloy actuator is a function of its modulus which varies with temperature such that the equilibrium position of the flow control valve changes in response to the outlet water temperature to vary the additional input flow of cold water to the heater tank.

The memory alloy actuator may be in the form of a helical coil capable of changing length as the stiffness (modulus) changes in response to the outlet water temperature to adjust the position of the control valve. In this way, the memory alloy actuator responds rapidly with the result that hot shots associated with wax element type actuators when the water temperature is adjusted or when the heater is re-started shortly after being shut down may be significantly reduced if not eliminated.

The reaction time of the memory alloy actuator may be further enhanced when it is used in conjunction with a relatively low capacity heater tank.

For example, instantaneous electric water heaters used for ablutionary showers typically have a heater tank capacity of about 25Occs and the present invention using a memory alloy actuator to control the inlet control valve can be employed with heater tanks having a capacity as low as 20ccs.

We have found that a heater tank with a low capacity of the order of 2Occs can reach a selected water temperature within 1 second of turning the unit on. This compares with 20 seconds for a typical instantaneous water heater employing a larger capacity heater tank without the inlet control valve of the present invention.

This is of particular benefit in a variety of applications where instantaneous water heaters are used to provide a source of hot water on demand. For instance, the present invention enables instantaneous electric water heaters for showering and hand washing to give an immediate supply of hot water to the user without waiting for hot water to feed through.

It has been noted with electric showers that users will often switch the shower on without getting under the spray so as to avoid being subjected to an initial spray of cold water. This can result in the user leaving the shower for some time to reach a stable condition before getting under the spray which is wasteful of water and energy.

It has also been noted with electric hand washers that users will not wait for hot water to feed through but use the initial cold stream for washing and then turn the unit off which may not provide adequate cleaning. This can be a particular problem where the hand washers are deployed in food preparation areas where regular hand cleaning is required for health and safety reasons to avoid contamination of food.

Preferably, the cold water by-pass is connected to an inlet at one end of the heater tank, typically the lower end, and the hot water outlet is provided at the opposite end or communicates with the opposite end of the heater tank.

In one embodiment, the cold water inlet control valve is connected to the same inlet as the cold water by-pass. For example, the cold water bypassing the cold water inlet control valve may be combined with the additional water from the cold water inlet control valve prior to input to the heater tank.

The cold water by-pass may be incorporated in the inlet control valve and combined with the additional flow from the inlet control valve within the valve body for delivery to the heater tank. Alternatively, the cold water by-pass may be separate from the inlet control valve and combined with the additional flow from the inlet control valve prior to entering the heater tank.

In another embodiment, the cold water inlet control valve is connected to another inlet separate from the inlet for the cold water by-pass. The inlet for the cold water inlet control valve may be spaced from the inlet for the cold water by-pass in the direction of flow of cold water through the heater tank.

In this way, the heat input to the heater tank has a reduced effect on the additional flow of cold water from the cold water inlet control valve. As a result, the effect of the additional flow of cold water on the temperature of the hot water flowing out of the heater tank is enhanced and response times may be reduced leading to improved temperature control and stability of the operating conditions. More specifically, the additional flow of cold water added to the heater tank from the inlet control valve combines with the flow of water from the cold water by-pass and provides a negative feed back effect that not only reduces further increase in water temperature but may lead to a reduction in water temperature.

Where the inlet for the cold water inlet control valve is separate from the inlet for the cold water by-pass, it may be located at any position between the inlet for the cold water by-pass and the outlet for hot water from the heater tank. Preferably, the inlet for the cold water control valve is positioned closer to the hot water outlet than the cold water bypass inlet and may be arranged substantially at the outlet.

Where the inlet for the cold water inlet control valve is separate from the inlet for the cold water by-pass, a plurality of separate inlets may be provided for adding cold water from the cold water inlet control valve at several locations axially and or circumferentially spaced apart. In this way, the additional flow of cold water may be controlled to optimise mixing and control of the outlet water temperature.

Advantageously, the cold water by-pass includes a flow regulator for maintaining a fixed or constant flow rate of cold water by-passing the inlet control valve for supply to the heater tank. As a result, the additional flow of cold water from the inlet control valve modulates the flow of cold water flowing through the heater tank.

The additional flow of cold water from the inlet control valve may be split and a small proportion directed within the vicinity of the temperature responsive actuator in order to provide negative feedback. In this way, response times may be further enhanced.

Preferably, the inlet control valve is a pressure balanced valve having a valve member axially movable relative to a valve seat to open and close a transfer port in response to axially opposed forces applied to the valve member by the biasing element and by the temperature responsive actuator. In this way, operation of the inlet control valve is independent of any variations in the pressure of the cold water supply.

The biasing element may be a return spring. The spring biasing may be adjustable, for example by a user operable control such as a knob or lever, to vary the actuator force required to overcome the biasing and open the cold water inlet control valve. In this way, the output temperature of the hot water from the heater tank may be adjusted according to user selection.

Alternatively, the biasing element may be a temperature responsive actuator exposed to the cold water inlet temperature. This actuator may be a memory alloy actuator similar to the memory alloy actuator responsive to the outlet water temperature. In this way, the actuator responsive to the cold water inlet temperature adjusts the force required to open the cold water inlet control valve in response to changes in temperature of the incoming cold water supply.

In one embodiment, the temperature responsive actuator is arranged externally of the heater tank. In another embodiment, the temperature responsive actuator is arranged internally of the heater tank.

In another arrangement, the first means comprises a cold water by-pass that includes a flow regulator for adjusting the flow rate to vary the outlet water temperature up to a pre-determined temperature and the second means comprises an inlet control valve that is operable in response to the outlet water temperature to provide an additional flow of cold water if the outlet water temperature exceeds the pre-determined temperature.

Preferably, the inlet control valve controls the additional flow of cold water into the heater tank by sensing the outlet water temperature via a temperature responsive actuator which controls opening/closing of the valve to control the additional input flow. The valve may be a pilot operated diaphragm valve with the actuator controlling opening closing of a pilot hole. The actuator may be a bi-metallic actuator movable between two positions to open and close the pilot hole in response to the outlet water temperature.

In this way the inlet control valve prevents the outlet water temperature exceeding the pre-determined temperature by providing an additional flow of cold water to reduce the outlet water temperature. As a result, the outlet water temperature from the heater tank is prevented from exceeding a safe level no matter what the temperature of the input water may be or if inlet water pressure and/or power input to the water heater changes.

The pre-determined outlet water temperature may be set according to the requirements for a particular installation. In ablutionary installations such as showers and hand washers, the pre-determined temperature may be set to reduce the risk of scalding. A temperature of 41-42 C may be suitable for most users but a lower temperature may be chosen for installations used in hospitals, schools or care homes where the users may be elderly or children or disabled.

Preferably, the additional cold water from the cold water inlet control valve is added to the heater tank close to the outlet so as to reduce the response time when the outlet water temperature exceeds the predetermined temperature.

In either arrangement, the power input to the heater tank may be provided by any suitable energy source for example electricity, gas or oil.

Preferably, the heater tank is provided with one or more electrical heating elements.

The heating elements may be printed circuit heating elements applied to a surface of the heater tank over which the water flows. Alternatively, the heating elements may be resistance heating elements positioned within the heater tank over which the water flows.

The power input may be fixed or adjustable. For example, a user operable control may be provided for user selection of the power input.

In this way, for a selected outlet water temperature, the flow rate may be altered by adjusting the power input. In this way, for application to showers, the spray force may be altered.

According to a second aspect of the present invention, there is provided a method of controlling the outlet water temperature from a heater tank of an instantaneous water heater by providing a cold water inlet control valve responsive to the outlet water temperature from the heater tank and a cold water input to the heater tank by-passing the inlet control valve and controlling the inlet control valve to provide an additional input of cold water to the heater tank in response to the outlet water temperature.

The cold water input by-passing the inlet control valve may be fixed and the additional input from the inlet control valve adjustable in accordance with user selection of any one of a range of outlet water temperatures.

Alternatively, the cold water input by-passing the inlet control valve may be adjustable in accordance with user selection of any one of a range of outlet water temperatures and the additional input from the inlet control valve operable to prevent the outlet water temperature exceeding a predetermined temperature.

According to a third aspect of the present invention, there is provided an instantaneous water heater comprising a water heater tank, a water inlet control valve for controlling the addition of water to the heater tank in response to the outlet water temperature from the heater tank, and cold water input by-passing the water inlet control valve for supplying water to the heater tank independently of the control valve.

Preferably the control valve is built into the heater tank and includes a temperature responsive actuator within the heater tank.

According to a fourth aspect of the present invention, there is provided an instantaneous water heater comprising a water heater tank for heating water flowing therethrough, a water inlet control valve for inputting water to the heater tank, and a memory alloy actuator responsive to the outlet water temperature from the heater tank for controlling the water inlet control valve.

According to a fifth aspect of the present invention, there is provided an instantaneous water heater comprising a water heater tank for heating water flowing therethrough, the tank having a water outlet and at least two separate water inlets.

According to a sixth aspect of the present invention, there is provided an instantaneous electric water heater comprising a heater tank having a water inlet and a water outlet, user operable means for adjustable selection of the outlet water temperature, a control valve for inputting water to the heater tank, thermostatic control means responsive to the outlet water temperature for controlling input of water to the heater tank by the control valve, and means by-passing the control valve for inputting water to the heater tank.

According to a seventh aspect of the present invention, there is provided an instantaneous electric water heater comprising a beater tank and a control valve built into the heater tank for controlling a supply of water to the heater tank in response to the outlet water temperature.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings wherein: Figure 1 shows an instantaneous electric water heater according to a first embodiment of the invention with parts of the inlet control valve being shown in section; Figure 2 is a section through the water inlet control valve shown in Figure 1; Figure 3 shows a modification to the instantaneous electric water heater shown in Figures 1 and 2; Figure 4 shows an instantaneous electric water heater according to a second embodiment of the invention with parts of the heater tank and inlet control valve being shown in section; Figure 5 shows a detail of the inlet control valve of Figure 4 to an enlarged scale; and Figure 6 shows an instantaneous electric water according to a third embodiment of the invention.

With reference to Figures 1 and 2 of the accompanying drawings, there is shown an instantaneous electric water heater including a heater tank 1 and a water inlet control valve 2. The water heater may be employed in an ablutionary installation to provide a source of hot water for a shower or hand washer.

The tank 1 has a cold water inlet 3 at the bottom and a hot water outlet 4 at the top. In this embodiment, the tank 1 is of rectangular shape with printed circuit heating elements (not shown) on one or both side walls qf the tank 1. The side walls are closely spaced to provide a thin, slimline construction of tank 1 having a volume of approximately 20ccs.

The water inlet control valve 2 has a pair of cold water inlets 5, 6 and a cold water outlet 7. The inlets 5, 6 are connected to an incoming cold water supply, for example mains cold water, via an on/off valve (not shown) operable by the user. The outlet 7 is connected to the inlet 3 to the heater tank 1.

One of the inlets 5 is provided with a flow regulator 8 operable to provide a minimum fixed flow rate at the outlet 7. The flow regulator 8 may be of any suitable type and in this embodiment comprises an 0-ring 9 surrounding a central core 10 provided with a series of longitudinal grooves (not shown) in the outer surface that define with the 0-ring 9 flow passages. The 0-ring 9 is deformable in response to changes in the water pressure to vary the cross-sectional area of the flow passages to maintain the minimum fixed flow rate.

The other inlet 6 communicates with the outlet 7 via a pressure balanced valve 11 responsive to the outlet water temperature from the heater tank 1. The valve 11 comprises a poppet valve member 12 biased at one end by a return spring 13 to a closed position in which a sealing element 14 carried by a valve head 15 engages an annular valve seat 16 closing a transfer port 17 to isolate the inlet 6 from the outlet 7.

The water inlet control valve 2 also has a hot water inlet 18 connected to the hot water outlet 4 from the heater tank 1 and a hot water outlet 19.

The hot water outlet 19 may be connected to an outlet fitting of a shower or hand washer. For example, the outlet 19 may be connected to a shower handset (not shown) via a flexible hose (not shown).

The other end of the poppet valve member 12 is operatively connected to an actuator 20 positioned in a chamber 21 between the hot water inlet 18 and hot water outlet 19. The actuator 20 comprises a helical coil 22 of memory alloy having elastic properties responsive to the temperature of the output hot water from the heater tank 1 to adjust the force applied by the coil 22 to the poppet valve member 12 that opposes the biasing of the return spring 13. In this embodiment, the coil 22 is a nickel/titanium alloy having a modulus (stiffness) that increases with temperature to vary the force applied to the poppet valve member 12 opposing the biasing of the return spring 13.

The return spring 13 acts between the poppet valve member 12 and a spring seat 23. A setting member 24 threadably engages the spring seat 23 and is rotatable via a user operable control such as a temperature control knob or lever (not shown) to axially adjust the position of the spring seat 23 to set the actuating force required to overcome the biasing of the return spring 13 to move the poppet valve member 12 to open the transfer port 17.

The actuating force applied to the poppet valve member 12 is dependent on change in stiffness (modulus) of the actuator 20 which in turn is dependent on the temperature of the output hot water from the heater tank 1. In this way, the user can adjust the outlet water temperature at which the transfer port 17 is opened.

In use, when the water heater is switched on, the control valve 2 is closed and cold water is initially introduced in to the heater tank 1 via the flow regulator 8 which ensures a minimum fixed flow rate that bypasses the inlet control valve 2.

A device (not shown) is provided to detect the presence of water either prior to or after energy has been applied via the heating elements to the water flowing through the heater tank 1. Devices that assume the presence of water prior to the energy being applied normally take the form of a diaphragm pressure or flow switch but could also be an electronic flow detector. A device that detects that no water is present after the application of energy could take the form of a heat sensitive switch, typically a bimetal switch that senses the temperature of the heating elements.

When the temperature of the hot water from the heater tank 1 exceeds that set by the user via the setting member 24, the force applied to the poppet valve member 12 by change in stiffness (modulus) of the actuator 20 overcomes the biasing of the return spring 13 and moves the poppet valve member 12 to open the transfer port 17 allowing cold water to flow from the inlet 6 to the outlet 7 to supplement the flow of cold water from the flow regulator 8.

In this way, the flow of cold water through the tank 2 is increased to maintain the selected temperature of the outlet water from the heater tank 1. The water heater may include a user operable control to allow the user to select different power settings to vary the flow rate and thus the spray force for any selected temperature of the outlet water from the heater tank 1.

The inlet control valve 2 has a high-pressure diaphragm 25 and a lowpressure diaphragm 26 which balance the forces of pressurised water across the valve 2 and the transfer port 17 so that no matter what pressure is applied, the resultant forces are substantially zero. In this way, the forces generated by the actuator 20 and the return spring 13 are the only forces that control the operation of valve 2.

More particularly, the diaphragms 25, 26 are sized so as to be the same effective diameter as the poppet valve sealing element 14 and valve seat 16. There are three pressure levels to be balanced. The first, and highest, is the mains inlet water pressure that acts on the diaphragm 25 to open the control valve 2 and on the poppet valve member 12 to close the control valve 2. As the diameters are equivalent, the inlet water pressure forces are balanced and there is no resultant force acting on the valve mechanism. The next highest pressure region is the inlet water pressure to the heater tank 1. This acts on the poppet valve member 12 to open the control valve 2 and on the diaphragm 26 to close the control valve 2.

Again the effective diameters are the same so there is no resultant force due to the inlet water pressure to the heater tank 1 influencing the position of the poppet valve member 12. The third pressure region is the outlet water pressure from the heater tank 1 which is also the inlet water pressure to a shower spray or similar. The outlet pressure which acts on the memory ahoy actuator side of diaphragm 26 and tends to open the poppet valve member 12 may be substantially balanced by connecting chamber 27 containing the return spring 13 and acting on diaphragm 25 tending to close poppet valve member 12 to atmosphere via inlet 28. In this way, the hydraulic pressures tending to influence the position of the poppet valve member 12 can be substantially balanced.

In some cases, however, the shower spray can become partially blocked, for example due to limescale deposits, particularly where there is hard water, and this could give rise to a significant outlet pressure acting on the diaphragm 26 tending to open the poppet valve member 12.

Accordingly, in a modification (not shown), the outlet waterway from the heater tank 1 may be connected to the chamber 27 to balance any change in the outlet pressure acting on diaphragm 26.

If the temperature of the outlet water from the heater tank 1 increases or decreases due to changes in inlet water temperature or voltage or any other reason, then the actuator 20 senses the change and adjusts the opening of the control valve 2 in order that the system is brought to anew equilibrium condition at predominantly the same user set temperature.

In this way, the outlet water temperature is thermostatically controlled by modulating the flow of cold water through the control valve 2 in addition to the minimum fixed flow of cold water that by-passes the control valve 2.

In the above-described embodiment, the heater tank 1 has a relatively low volume of approximately 20ccs. As a result, changes in the outlet water temperature from the heater tank 1 can be compensated in a relatively short period of time by combining the additional flow of cold water from the control valve 2 with the fixed flow from the inlet 5 for input to the inlet 3 at the bottom of the heater tank 1 so as to be hardly noticeable to the user.

We have found that the heater tank 1 can reach a selected water temperature within 1 second of turning the unit on and when changing the selected temperature in use. Furthermore, the selected water temperature is maintained substantially constant in response to changes in any one of the water pressure, inlet water temperature and mains voltage.

Moreover, on shut-down, hot water is flushed from the heater tank 1 and the residual heat of the heating elements dissipated. As a result, hot shots in use of the water heater and when re-starting the water heater can be reduced if not eliminated.

Referring now to Figure 3 of the drawings, there is shown a modification of the embodiment above-described in which like reference numerals in the series 100 are used to indicate corresponding parts.

In this embodiment, the heater tank 101 is of cylindrical shape containing one or more electrical heating elements (not shown) and has a larger volume of approximately 25Occs. The heating elements extend from the upper end of the heater tank 101 to the lower end and may be linear rods or coils.

The inlet 105 of cold water inlet control valve 102 is closed with a blanking plug 130 and the incoming cold water supply to the inlet 106 is provided with a cold water branch 131 by-passing the valve 102 and connected to cold water inlet 103 at the bottom of the heater tank 101.

The inlet 103 is provided with a flow regulator (not shown) operable to provide a minimum fixed flow rate to the inlet 103 of the heater tank 101.

The outlet 107 for the modulating flow of cold water from the control valve 102 is connected to a separate cold water inlet 132 spaced above the inlet 103 and closer to the hot water outlet 104.

With this arrangement, the portion of the heating elements extending below the inlet 132 towards the bottom of the heater tank 101 is subjected to a relatively low fixed flow of cold water whilst the portion extending above the inlet 132 towards the top of the heater tank 101 is subjected to the fixed flow of water from the inlet 103 at the bottom of the heater tank 101 plus the additional flow from the inlet 132.

Injecting the additional flow of cold water from the control valve 102 closer to the outlet 104 from the heater tank 101 allows direct control of the top heated portion of the relatively larger capacity heater so that a faster response to changes in the outlet water temperature from the heater tank 101 can be achieved without oscillation of the outlet water temperature.

The volume of the top heated portion of the heater tank 101 can be adjusted by altering the position of the inlet 132 to vary the thermal inertia produced by the volume of heated water, which allows the system to achieve inherent stability.

In a modification (not shown), the additional input flow of cold water to the heater tank in Figures 1 and 3 may be split prior to adding to the heater tank and a small proportion diverted directly into the chamber containing the memory alloy actuator. This may assist in making the

system more stable.

The proportional split may be made by directing the regulated input flow through a relatively small area aperture into the chamber containing the memory ahoy actuator and a relatively larger area aperture into the heater tank. Since the pressure prior to these apertures is equal, the rates of flow of water is proportional to their respective aperture areas. A proportional split in the order of 6:1 - heater tank to memory alloy actuator chamber - has been found to give good results.

Referring to Figures 4 and 5 of the drawings, there is shown a second embodiment of an instantaneous water heater according to the present invention. For convenience, like reference numerals in the series 200 are used to indicate parts corresponding to the embodiment shown in Figures 1 to 3. In this embodiment, the cold water inlet control valve 202 is built-into the heater tank 201 with the coil 222 of memory alloy located inside the heater tank 201 in the direction of flow of water through the heater tank 201 to provide thermostatic control of the outlet water temperature via change in modulus (stiffness) of the coil 222.

As shown, the upper end of the heater tank 201 is closed by a lid 233 provided with an electric heating element in the form of a helical coil 234 that extends from the upper end to the lower end of a heat exchange chamber 235 within the heater tank 201. Cold water inlet 203 is arranged at the lower end of the heat exchange chamber 235 for connection to a cold water supply such as the incoming mains cold water supply and is provided with a flow regulator (not shown) or similar device for inputting cold water having a substantially constant flow rate to the heat exchange chamber 235. More than one helical coil 234 may be provided to allow user selection of different power inputs to the heater tank 201.

The heater tank 201 is provided with an internal outlet port (not shown) at the upper end of the heat exchange chamber 235 above the helical heater coil 234 that opens into a passageway (not shown) that extends axially to the lower end of the heater tank 201 and terminates in outlet 204 for delivery of heated water from the heater tank 201. The outlet 204 may provide a supply of hot water to a shower or a hand washer or other ablutionary fitting. In a modification (not shown) the outlet 204 may be provided at the upper end of the heater tank 204 as in the previous embodiments.

The inlet control valve 202 is mounted in a fluid tight manner in a through hole at the lower end of the heater tank 201 and has a cold water inlet 206 for connection to the cold water supply externally of the heater tank 201. Both inlets 203, 206 are connected to the cold water supply via a common inlet (not shown) and an on/off valve (not shown) such as a solenoid valve for starting and stopping water flow through the heater.

The inlet control valve 202 is biased to the closed position illustrated by return spring 213 acting on valve member 212 via spring seat 223 and diaphragm 225 to urge valve member 212 to engage valve seat 216 and close transfer port 217. The transfer port 217 opens into an elongate guide tube 236 arranged to extend towards the upper end of the heater tank 201 within the heater coil 234.

The guide tube 236 slidably supports an actuator rod 237. The lower end of the actuator rod 237 bears on the valve member 212. The upper end of the actuator rod 237 projects from the guide tube 236 and supports the temperature responsive actuator 220 for the inlet control valve 202 at the upper end of the heater tank 201 adjacent to the outlet port.

The actuator 220 comprises helical coil 222 of memory alloy that is guided axially in an open sleeve 239 at the upper end of the guide tube 236 and is retained at the free end by an inwardly turned flange 240. The actuator rod 237 is axially movable to open the inlet control valve 202 against the biasing of the return spring 213 in response to change in modulus (stiffness) of the memory alloy coil 222 when the outlet water temperature sensed by the memory alloy coil 222 exceeds the selected temperature.

In this embodiment, the actuator coil 222 is surrounded by the upper end of the heater coil 223 and the heater tank 201 is provided with a flow guide (not shown) at the upper end of the heater coil 223 that causes the water to flow inwards over and through the actuator coil 222. In a modification (not shown), the actuator coil 222 is supported above the upper end of the heater coil 223 and the water is again guided over and through the actuator coil 222 by a flow guide.

The actuator rod 237 is provided with an 0-ring (not shown) in a groove 238 to provide a sliding seal between the actuator rod 237 and guide tube 236. Between the lower end and the 0-ring, the acWator rod 237 is substantially of X-shape in transverse cross-section to provide four elongate channels 241 (one only shown) extending lengthwise of the actuator rod 237 along which water can flow when the inlet control valve 202 is open. It will be understood that the actuator rod may have any suitable shape that permits water to flow to the holes in the guide tube 236.

The guide tube 236 is provided with a plurality of holes (not shown) through which water in the channels 241 can flow out of the guide tube 236 into the stream of water flowing through the heat exchange chamber 235 at a plurality of positions spaced apart circumferentially and axially of the guide tube 236 along the length of the heat exchange chamber 235.

The amount of water injected into the heat exchange chamber 235 is controlled by movement of the valve member 212 to open the inlet control valve 202 in response to the outlet water temperature sensed by the coil 222 of memory alloy.

The inlet control valve 202 is pressure balanced to substantially reduce or eliminate the effects of water pressure on the movement of the valve member 212 by the diaphragm 225 on the inlet side being sized to match the effective diameter of the valve member 212 and by the 0-ring on the outlet side. In this way, operation of the valve 202 is controlled by the opposing forces of the return spring 223 and actuator coil 222 of memory alloy and is substantially unaffected by changes in the water pressure.

The force applied to the valve member 212 by the spring 213 to close the inlet control valve 202 is adjustable via setting member 224 for user selection of the outlet water temperature and the actuator 220 is operable to open the inlet control valve 202 when the force applied to the valve member 212 by the memory alloy coil 222 overcomes the set force of the spring 213 to inject water into the heat exchange chamber 235 through the holes in the guide tube 236.

With this arrangement, the injected water modulates the water flow over substantially the whole length of the heater coil 223 and provides a rapid response to correct any detected difference between the outlet water temperature sensed by the actuator coil 222 and the selected outlet water temperature. As a result, on start-up, the selected outlet water temperature is achieved quickly and is maintained substantially constant irrespective of changes in the pressure of the water supply or the inlet water temperature or the voltage of the power supply to the heater coil 223. In this way, thermostatic control of the outlet water temperature may be enhanced.

The holes may be of the same size and uniformly spaced apart in an even or regular pattern to distribute the added water uniformly along the length of the heater coil 223. Alternatively, the size and/or spacing may be chosen to provide any desired pattern of holes to vary the amount of water added to the heat exchange chamber 235 along the length of the heater coil 223, for example to increase the water input from the holes in the direction of flow through the heat exchange chamber 235. In this way, the arrangement of the holes may be chosen to optimise the response and stability of the heater tank 201.

Referring now to Figure 6 of the drawings, a third embodiment of a water heater according to the invention is shown. The water heater may be employed in an ablutionary installation to provide a source of hot water for a shower or hand washer.

The water heater 351 has a cylindrical heater tank 352 with a cold water inlet 353 at the lower end, a cold water inlet 354 at the upper end, and a hot water outlet 355 exiting from the bottom of the heater tank 352.

The hot water outlet 355 is provided at one end of an internal tube (not shown) that extends lengthwise of the heater tank 352 and terminates with the other, open end of the tube adjacent to the top of the heater tank 352.

In this way, cold water admitted via the inlet 353 flows up through the heater tank before entering the open end of the tube at the upper end of the heater tank 352 and flowing down through the tube to the outlet 355.

The heater tank 352 contains one or more electrical heating elements (not shown) for heating water flowing therethrough. The heating elements extend from the upper end of the heater tank 352 to the lower end and may be linear rods or coils.

The water heater includes a flow control valve 356 having an inlet 357 connectable to a cold water source, for example mains cold water and an outlet 358 connected to the cold water inlet 353 at the lower end of the heater tank 352.

The flow control valve 356 includes a spindle 359 for a manually operable control knob or lever (not shown) by means of which a user can adjust a flow regulator (not shown) to vary the flow rate of cold water delivered from the outlet 358 of the flow control valve 356 to the inlet 353 of the heater tank 352.

In this way, the user can adjust the temperature of the hot water from the heater tank 352 for a given power input to the heater tank 352. The power input may be adjustable to allow the user to select different flow rates for a given water temperature.

The flow control valve 356 has a further outlet 360 arranged to by-pass the flow regulator and provide a supply of cold water to a cold water inlet control valve 361.

The cold water inlet control valve 361 has a cold water inlet 362 connected to the outlet 360 of the flow control valve and a cold water outlet 363 connected to the cold water inlet 354 at the upper end of the heater tank 352.

The cold water inlet control valve 361 also has a hot water inlet 364 connected to the hot water outlet 355 from the heater tank 352 and a hot water outlet 365. The hot water outlet 365 may be connected to an outlet fitting of a shower or hand washer. For example, the outlet 365 may be connected to a shower handset (not shown) via a flexible hose (not shown).

The cold water inlet control valve 361 further includes a temperature responsive actuator in the form of a snap action bi-metallic disc (not shown) arranged to monitor the temperature of the hot water from the heater tank 352 and control the flow of cold water by-passing the flow regulator to the heater tank 352.

The bi-metallic disc controls opening/closing of a small pilot hole of a diaphragm-operated valve (not shown) which in turn controls water flow between the cold water inlet 362 and cold water outlet 363 of the inlet control valve 361.

The diaphragm operated valve is closed to prevent flow of cold water to the cold water inlet 354 when the disc closes the pilot hole and is opened to allow flow of cold water to the inlet 354 when the disc opens the pilot hole.

The pilot hole is closed by the disc up to a pre-determined temperature of the hot water exiting the heater tank 352 at which it snaps over to open the pilot hole and allow cold water by-passing the flow regulator to be injected into the upper end of the heater tank 352 via the inlet 354.

For example, in an ablutionary installation such as a shower or hand washer, the bi-metallic disc may be set to snap over at a temperature above which it is considered too hot for water to be applied directly to the skin (in the order of 45 Deg Celsius).

In this way, the cold water injected through the inlet 354 is not subjected to the full effect, of the heating elements within the heater tank 352 and mixes with and cools the outfiowing water from the heater tank 352 prior to flowing past the bi-metallic disc.

Consequently, once sufficient cold water has been injected to cool the outfiowing hot water to the pre-determined temperature, the bi-metallic disc snaps back again and the flow of cold water to the inlet 354 ceases.

If the user does not adjust the temperature down or other conditions cause the temperature to rise again, then the device will continue to cycle on and off, thereby limiting the output temperature of the hot water from the heater tank 352 to a safe level.

In use, when the water heater is switched on, the diaphragm-operated valve is closed to isolate the inlet 354 at the upper end of the heater tank 352 and cold water is introduced in to the heater tank 352 via the flow regulator of the flow control valve 356 by-passing the cold water inlet control valve 361.

An on-off valve may be provided up-stream of the flow control valve 356 or the flow regulator may be operable to shut-off the water flow. A device (not shown) is provided to detect the presence of water prior to energy being applied to the heating elements to the water flowing through the heater tank 352. Such device normally takes the form of a diaphragm pressure or flow switch but could also be an electronic flow detector.

The user adjusts the flow regulator to vary the flow rate and hence the outlet temperature of the hot water from the heater tank 352 for a given power input to the heater tank 352.

If the outlet temperature of the hot water from the heater tank 352 exceeds the pre-determined safe temperature, the bi-metallic disc snaps over to open the pilot hole controlling the diaphragm-operated valve.

As a result, cold water bypassing the flow regulator is injected into the heater tank 352 to reduce the temperature of the hot water flowing out of the heater tank 352 to a safe level.

As will now be appreciated, the above-described water heaters employ a cold water inlet control valve for controlling addition of cold water to the heater tank in response to the temperature of the water output from the heater tank.

In the embodiments of Figures 1 to 5, a fixed flow of cold water is provided that by-passes the control valve and the control valve is operable to adjust the amount of cold water added to the fixed flow to maintain constant a selected temperature of the outlet water.

In the embodiment of Figure 6, a variable flow of cold water is provided that by-passes the control valve for adjusting the selected temperature of the outlet water and the control valve is operable to prevent the outlet water temperature exceeding a pre-determined safe limit to any appreciable extent.

It will be understood that the invention is not limited to the embodiments above-described and that various improvements or modifications can be made.

For example, the arrangement of two separate cold water inlets to the heater tank in Figures 3 and 4 may be applied to the heater tank of Figure 1. This may allow the capacity of the heater tank to be increased whilst maintaining its stability and reaction time when using printed circuit heating elements in place of traditional electrical resistance heaters located within the heater tank.

The memory alloy actuator of the cold water inlet control valves of Figures 1 to 5 could be replaced with any other type of temperature responsive actuator having a suitable response time.

The cold water inlet control valve of Figures 1 to 5 could incorporate a secondary memory alloy actuator on the input side of the valve which compensates for changes in the temperature of the cold water supply by adjusting the force required to open the valve by the actuator responsive to the outlet water temperature in proportion to the temperature of the incoming cold water.

The pressure balanced valve could be of any other suitable type, for example a pilot assisted diaphragm valve or a poppet valve fed from a pressure regulator or a flow regulating core type valve.

Where a separate inlet is provided for the additional cold water flow to the heater tank from the water inlet control valve, a single inlet may be provided as in the embodiment of Figure 3 or multiple inlets may be provided as in the embodiment of Figures 4 and 5.

Where multiple inlets are provided they may be spaced apart axially and/or circumferentially to provide any desired flow pattern within the heater tank to optimize mixing and control of the temperature of the outfiowing water.

The inlet control valve may be built-into the heater tank as shown in Figures 4 and 5 with the actuator coil located inside the heater tank or it may be separate as shown in Figures 1 to 3 with the actuator coil arranged externally of the heater tank.

Where the control valve is built into the heater tank as shown in Figures 4 and 5, it may be arranged to input water into the heater tank at a plurality of positions as described or at a single position.

The bi-metallic disc used in Figure 6 could be replaced by any other type of temperature responsive actuator to control the addition of cold water to the heater tank. The actuator could control a pilot operated diaphragm as described or any other suitable valve.

Alternatively, the actuator could be of any other suitable type. For example, a device which sensed an over temperature using an electric bimetal switch which then allowed a solenoid operated valve to inject the additional flow in to the top of the heater tank.

In the above-described embodiments, the water heaters are described employing electrical heating elements to heat the water flowing through the heater tank. It will be understood, however that this is not essential and that other energy sources could be employed such as gas or oil.

As used herein the terms "cold water" and "hot water" are used for convenience only and refer to the water supplied to the inlet(s) of the heater tank (cold water) and water delivered from the outlet of the heater tank (hot water) where the inlet water is colder than the outlet water.

The terms are relative and indicate the temperature difference of the water and are not intended to indicate any particular temperatures.

Claims

1. An instantaneous water heater comprising a water heater tank for heating water, first means for adjusting the flow rate of cold water supplied to an inlet of the heater tank in accordance with user selection of the outlet water temperature, and second means responsive to the outlet water temperature from the heater tank for supplying cold water to a second inlet of the heater tank if the outlet water temperature exceeds a pre-determined limit.

2. An instantaneous water heater according to claim 1 wherein the first means comprises a flow regulator for adjusting the flow rate to provide any selected one of a range of outlet water temperatures, and the second means is operable to provide an additional flow of cold water to the heater tank if the outlet water temperature exceeds the pre-determined limit.

3. An instantaneous water heater according to claim 2 wherein, the second means comprises a valve and a temperature responsive actuator arranged to sense the outlet water temperature and control opening/closing of the valve to control the additional flow of cold water to the heater tank.

4. An instantaneous water heater according to claim 3 wherein the valve is a pilot operated diaphragm valve with the actuator controlling opening closing of a pilot hole.

5. An instantaneous water heater according to claim 4 wherein the actuator is a bi-metallic actuator movable between two positions to open and close the pilot hole in response to the outlet water temperature.

6. An instantaneous water heater according to any one of the preceding claims wherein, the heater tank has an outlet and the second inlet is close to the outlet so as to reduce the response time when the outlet water temperature exceeds the pre-determined limit.

7. An instantaneous water heater according to any one of the preceding claims wherein a power input to the heater tank is provided by any one of electricity, gas or oil.

8. An instantaneous water heater according to claim 7 wherein, the heater tank is provided with one or more electrical heating elements.

9. An instantaneous water heater according to claim 8 wherein the or each heating element is a printed circuit heating element applied to a surface of the heater tank over which the water flows.

10. An instantaneous water heater according to claim 8 wherein the or each heating element is a resistance heating element positioned within the heater tank over which the water flows.

11. An instantaneous water heater according to any one of claims 7 to 10 wherein the power input is fixed.

12. An instantaneous water heater according to any one of claims 7 to 10 wherein the power input is adjustable.

13. An instantaneous water heater substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

14. A method of limiting the outlet water temperature from a heater tank of an instantaneous water heater by providing a cold water inlet control valve responsive to the outlet water temperature from the heater tank and a cold water input to the heater tank by-passing the inlet control valve, adjusting the cold water input according to user selection of any selected one of a range of outlet water temperatures, and controlling the inlet control valve to provide an additional input of cold water to the heater tank if the outlet water temperature exceeds a pre-determined limit.

15. A method of limiting the outlet water temperature from a heater tank of an instantaneous water heater substantially as hereinbef ore described with reference to Figure 6 of the accompanying drawings.

16. An instantaneous water heater comprising a water heater tank, first means for supplying cold water to the heater tank, and second means for supplying cold water to the heater tank, the first means providing a substantially constant flow rate and the second means providing a variable flow rate additional to the flow rate of the first means in response to the outlet water temperature from the heater tank whereby the flow of water supplied to the heater tank can be varied to maintain a selected water temperature substantially constant.

17. An instantaneous water heater according to claim 16 wherein, the second means comprises an inlet control valve operable in accordance with user selection of a desired outlet water temperature.

18. An instantaneous water heater according to claim 17 wherein, the inlet control valve controls the additional flow of cold water into the heater tank by sensing the output temperature via an actuator which directly acts on the valve to control the additional input flow.

19. An instantaneous water heater according to claim 18 wherein, the inlet control valve controls its own input flow dependent on the output temperature from the heater tank such that the temperature within the heater tank remains predominantly the same as the user selected output temperature no matter what the temperature of the input water may be.

20. An instantaneous water heater according to claim 18 or claim 19 wherein, the actuator comprises a memory alloy having elastic properties responsive to the outlet water temperature and the flow control valve is operable in response to an applied force by the actuator to control the additional input flow.

21. An instantaneous water heater according to claim 20 wherein, the memory alloy actuator has a modulus that changes with temperature to vary an actuating force applied to the flow control valve.

22. An instantaneous water heater according to claim 21 wherein the memory alloy actuator has a modulus that increases with increase in temperature.

23. An instantaneous water heater according to any one of claims 20 to 22 wherein the memory alloy comprises nickel/titanium alloys.

24. An instantaneous water heater according to any one of claims 20 to 23 wherein, the inlet control valve is biased towards a closed position by a biasing element that is opposed by the actuating force applied by the memory alloy actuator.

25. An instantaneous water heater according to claim 24 wherein, the inlet control valve adopts an equilibrium position where the biasing element and opposing memory alloy actuator coil are compressed by an amount according to the stiffness of the biasing element and the memory alloy actuator.

26. An instantaneous water heater according to claim 25 wherein the stiffness of the memory alloy actuator is a function of its modulus which varies with temperature such that the equilibrium position of the flow control valve changes in response to the outlet water temperature to vary the additional input flow of cold water to the heater tank.

27. An instantaneous water heater according to any one of claims 20 to 26 wherein the memory alloy actuator is in the form of a helical coil capable of changing length as the stiffness (modulus) changes in response to the outlet water temperature to adjust the position of the control valve.

28. An instantaneous water heater according to any one of claims 18 to 27 wherein the temperature responsive actuator is located within the heater tank.

29. An instantaneous water heater according to any one of claims 18 to 27 wherein the temperature responsive actuator is located outside the heater tank.

30. An instantaneous water heater according to any one of the preceding claims wherein the heater tank has a low volume of the order of 20ccs.

31. An instantaneous water heater according to any one of the preceding claims wherein, the first means is connected to an inlet at one end of the heater tank, and the hot water outlet is provided at the opposite end or communicates with the opposite end of the heater tank.

32. An instantaneous water heater according to claim 31 wherein, the second means is connected to the same inlet as the first means.

33. An instantaneous water heater according to claim 31 wherein, the second means is connected to another inlet separate from the inlet for the firs means.

34. An instantaneous water heater according to claim 33 wherein the inlet for the second means is spaced from the inlet for the first means in the direction of flow of cold water through the heater tank.

35. An instantaneous water heater according to claim 34 wherein the inlet for the second means can be located at any position between the inlet for the first means and the outlet for hot water from the heater tank.

36. An instantaneous water heater according to claim 34 or claim 35 wherein, the inlet for the second means is positioned closer to the hot water outlet than the inlet for the first means.

37. An instantaneous water heater according to claim 36 wherein, the inlet for the second means is arranged substantially at the outlet.

38. An instantaneous water heater according to any one of claims 33 to 37 wherein the second means is provided with a plurality of separate inlets for adding cold water at several locations axially and/or circumferentially spaced apart.

39. An instantaneous water heater according to any one of the preceding claims wherein the first means by-passes the second means for supplying cold water to the heater tank independently of the second means.

40. An instantaneous water heater according to any one of the preceding claims wherein, the first means includes a flow regulator for maintaining a substantially constant flow rate of cold water to the heater tank.

41. An instantaneous water heater according to claim 18 and any claim dependent on claim 18 wherein the additional flow of cold water from the inlet control valve is split prior to the heater tank and a small proportion added directly to a chamber containing the temperature responsive actuator.

42. An instantaneous water heater according to claim 18 and any claim dependent on claim 18 wherein, the inlet control valve is a pressure balanced valve.

43. An instantaneous water heater according to claim 42 as dependent on claim 24 wherein the pressure balanced valve has a valve member axially movable relative to a valve seat to open and close a transfer port in response to axially opposed forces applied to the valve member by the biasing element and by the temperature responsive actuator.

44. An instantaneous water heater according to claim 43 wherein the biasing element is a return spring.

45. An instantaneous water heater according to claim 44 wherein the spring biasing is adjustable.

46. An instantaneous water heater according to claim 45 wherein a user operable control is provided to vary the actuator force required to overcome the biasing and open the cold water inlet control valve such that the output temperature of the hot water from the heater tank may be adjusted according to user selection.

47. An instantaneous water heater according to claim 43 wherein, the biasing element is a temperature responsive actuator exposed to the cold water inlet temperature.

48. An instantaneous water heater according to claim 47 wherein the biasing element is a memory alloy actuator responsive to the cold water inlet temperature to adjust the force required to open the cold water inlet control valve in response to changes in temperature of the incoming cold water supply.

49. An instantaneous water heater according to any one of claims 16 to 39 wherein, the first means includes a flow regulator for adjusting the flow rate to vary the outlet water temperature up to a pre-determined temperature and the second means is operable in response to the outlet water temperature to provide an additional flow of cold water if the outlet water temperature exceeds the pre-determined temperature.

50. An instantaneous water heater according to claim 49 wherein, the second means controls the additional flow of cold water into the heater tank by sensing the outlet water temperature via a temperature responsive actuator which controls opening/closing of a valve to control the additional input flow.

51. An instantaneous water heater according to claim 50 wherein the valve is a pilot operated diaphragm valve with the actuator controlling opening closing of a pilot hole.

52. An instantaneous water heater according to claim 51 wherein the actuator is a bi-metallic actuator movable between two positions to open and close the pilot hole in response to the outlet water temperature.

53. An instantaneous water heater according to any one of claims 49 to 52 wherein, the additional flow of cold water is added to the heater tank close to the outlet so as to reduce the response time when the outlet water temperature exceeds the pre-determined temperature.

54. An instantaneous water heater according to any one of the preceding claims wherein the power input to the heater tank is provided by any one of electricity, gas or oil.

55. An instantaneous water heater according to claim 54 wherein, the heater tank is provided with one or more electrical heating elements.

56. An instantaneous water heater according to claim 55 wherein the or each heating element is a printed circuit heating element applied to a surface of the heater tank over which the water flows.

57. An instantaneous water heater according to claim 55 wherein the or each heating element is a resistance heating element positioned within the heater tank over which the water flows.

58. An instantaneous water heater according to any one of claims 54 to 57 wherein the power input is fixed or adjustable.

59. An instantaneous water heater according to claim 58 wherein a user operable control is provided for user selection of the power input.

60. A method of controlling the outlet water temperature from a heater tank of an instantaneous water heater by providing a cold water inlet control valve responsive to the outlet water temperature from the heater tank and a cold water input to the heater tank by-passing the inlet control valve, and controlling the inlet control valve to provide an additional input of cold water to the heater tank in response to the outlet water temperature.

61. A method according to claim 60 wherein the cold water input bypassing the inlet control valve is fixed and the additional input from the inlet control valve adjustable in accordance with user selection of any one of a range of outlet water temperatures.

62. A method according to claim 60 wherein, the cold water input bypassing the inlet control valve is adjustable in accordance with user selection of any one of a range of outlet water temperatures and the additional input from the inlet control valve is operable to prevent the outlet water temperature exceeding a pre-determined temperature.

63. An instantaneous water heater comprising a water heater tank, a water inlet control valve for controlling the addition of water to the heater tank in response to the outlet water temperature from the heater tank, and means by-passing the water inlet control valve for supplying water to the heater tank.

64. An instantaneous water heater comprising a water heater tank for heating water flowing therethrough, the tank having a water outlet and at least two separate water inlets, wherein one of the inlets is connected to a water inlet control valve and the other inlet is connected to a cold water by-pass for supplying cold water to the heater tank independently of the cold water inlet control valve.

65. An instantaneous electric water heater comprising a heater tank having a water inlet and a water outlet, user operable means for adjustable selection of the outlet water temperature, a control valve for inputting water to the heater tank, thermostatic control means responsive to the outlet water temperature for controlling input of water to the heater tank by the control valve, and means by-passing the control valve for inputting water to the heater tank.

66. An instantaneous water heater substantially as hereinbef ore described with reference to Figures 1 and 2 of the accompanying drawings.

67. An instantaneous water heater substantially as hereinbef ore described with reference to Figures 1 and 2 of the accompanying drawings as modified by Figure 3 of the accompanying drawings.

68. An instantaneous water heater substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.

69. An instantaneous water heater substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

70. A method of controlling the outlet water temperature from a heater tank of an instantaneous water heater substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

71. A method of controlling the outlet water temperature from a heater tank of an instantaneous water heater substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings as modified by Figure 3 of the accompanying drawings.

72. A method of controlling the outlet water temperature from a heater tank of an instantaneous water heater substantially as hereinbef ore described with reference to Figures 4 and 5 of the accompanying drawings.

73. A method of controlling the outlet water temperature from a heater tank of an instantaneous water heater substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.