GB2390136A - Instantaneous water heater flow regulation - Google Patents

Abstract

The amount of water flow through a second flow regulator 130 is controlled in dependence on the water temperature in portion 116 of a water flow path between a heat exchanger 14 and a mixer portion 140. A first flow regulator 120 may be manually controlled by a user to select the required water temperature. An increase in flow rate through regulator 120 decreases the water temperature at outlet 19. Conversely, a decrease in flow rate through regulator 120 increases the water temperature at outlet 19. The second flow regulator 130 is only opened if the temperature sensing portion 116 detects a rise above a predetermined maximum, such as caused by an increase in water inlet temperature or by a power surge in the heat exchanger. A by-pass 138 channels water to the mixer portion when the second regulator is opened to reduce the temperature of water at the outlet 19. The temperature sensing portion contains a sensor 118 such as a wax capsule or a bimetallic strip.

Description

-1 lNSTANTANEOUS WATER HEATER The present invention relates to an

instantaneous water heater, in particular an instantaneous water heater for use as part of an instantaneous electric shower.

5 A great variety of instantaneous water heater configurations are known. A heat exchanger used in an instantaneous water heater will heat water. For a given set of operating conditions, such as power and number of heating elements, the temperature reached by the water is dependent upon the amount of time the water spends in the heat exchanger. Thus, an increase of flow rate of water through a heat 10 exchanger results in a drop in the output temperature of the water from the heat exchanger. A problem with known instantaneous water heaters is that, for a fixed set of operating conditions, the output temperature of the water from the heat exchanger varies according to the temperature of the water input into the heat exchanger. Thus, 15 the flow rate of water through the heat exchanger which gives a comfortable output temperature on a cold day can give a dangerously high output temperature on a warm day. This can lead to a problem as follows: if a flow rate of water through the heat exchanger is selected for comfortable use on a cold day and the same setting is used on a warm day (i.e. the temperature selector is not adjusted), the user can unwittingly 20 select a dangerously high water output temperature. The present invention addresses this problem.

The present invention provides an instantaneous water heater comprising: an inlet; a heat exchanger for heating water; a first flow regulator for regulating the flow of water supplied to said heat exchanger from said inlet; a mixer portion for mixing 25 water heated by said water heater with unheated water from said inlet; and a second flow regulator for regulating the flow, to said mixing portion, of said unheated water from said inlet; wherein the water flow rate through one of said first or second flow regulators is automatically controlled according to the temperature of water at a predetermined position in said water heater thereby to compensate for variations in 30 the temperature of water at said inlet.

-2 Thus, the instantaneous water heater of the present invention can compensate for a variation in the temperature of water input into the heat exchanger in the following way: if the temperature at the predetermined position increases as a result of an increase in input water temperature, the one of the first and second flow 5 regulators is opened to allow an increased flow through it, thereby to reduce the temperature of water exiting the mixer portion.

Preferably, the predetermined position is upstream of the mixer portion. This allows compensation for variations in input water temperature without requiring knowledge of the position of the other of the first and second flow regulators.

10 The other of the first or second flow regulators may be adapted for user control to vary the flow of water through it and thereby vary the temperature of water output from the water heater.

Preferably, the one of the first or second flow regulators is mechanically controlled by a temperature - sensitive member at the predetermined position, the 15 temperature - sensitive member having a state which is dependent upon surrounding water temperature. In this way, there is no need for complicated and expensive control electronics and sensors.

If the one of the first or second flow regulators is the first flow regulator this arrangement can be used to keep the output temperature constant for a given flow 20 rate of water through the second regulator irrespective of variations in input temperature i.e. true thermostatic control. Furthermore, the compensation is fast as the temperature of the output water is directly controlled by the flow rate of water through the second regulator to the mixer portion.

Alternatively, if the one of the first or second flow regulators is the second 25 flow regulator, then when the water heater outlet temperature exceeds a predetermined limit, the second flow regulator may be automatically opened in proportion to the amount the predetermined temperature limit is exceeded. Thus, this arrangement may be used as a safety device to avoid scalding if the inlet water temperature is particularly high.

30 Preferably, said one of said first or second flow regulators comprises first and second movable members in first and second orifices for the flow of water

therethrough, said first and second movable members being coupled such that, on actuation, they move in opposite directions relative to the flow of water through said orifices, actuation of said movable members being effective to vary the flow rate of water through said flow regulator.

5 In this way, the amount of force required to move the first and second moveable members, and thereby to vary the flow rate of water through the flow regulator, is much reduced. This is because one of the flow members will be required to move against the inlet water pressure, while the other member moves with the inlet water pressure.

10 Preferably, the heat exchanger comprises a chamber having an inlet and an outlet, the inlet being attached to an output of said first flow regulator, and heating elements positioned in said chamber for heating water flowing from said inlet of said chamber to said outlet of said chamber.

In this case, preferably, the instantaneous water heater further comprises a 15 chimney positioned in said chamber defining at one end said outlet of said heat exchanger and at another end an outlet of said water heater. This arrangement is particularly compact, allowing the instantaneous water heater to be ergonomically pleasing. The present invention will now be described in more detail, by way of 20 example only, with reference to the accompanying drawings, in which: Figure 1 illustrates the front cover of an instantaneous water heater; Figure 2 illustrates an exploded view of the functional components of an instantaneous water heater; Figure 3 illustrates schematically the principle of temperature control in a by 25 pass type instantaneous water heater; Figure 4 illustrates a first embodiment of the present invention; Figure 5 illustrates a second embodiment of the present invention; Figure 6 illustrates a perspective view of components according to the first embodiment of the present invention; and 30 Figure 7 illustrates a schematically how the practical embodiment of Figure 6 is assembled.

- As illustrated in Figure 1, an instantaneous water heater includes a front cover 2 including a water temperature control 4 and an optional on/off button 6. The function of the on/off button 6 may also be incorporated into the temperature control 4. 5 The front cover 2 houses a number of functional components for providing hot water of a desired temperature.

Figure 2 illustrates a suitable arrangement of components. However, it should be appreciated that many other arrangements could be provided within the scope of the invention.

10 In the embodiment illustrated in Figure 2, an on/off flow control valve 20 operates under the control of a button 22a to control whether or not there is any flow from the inlets 8 or 10 to a heat exchanger 14. Within the heat exchanger 14, the water flows up around the outside of a chimney 16 in contact with a heater element 18. The water then flows down through the inside of the chimney 16 and out of an 15 outlet 19. Dependent upon the position of the on/off control valve 20 and/or flow of water through the water heater, an arm 24 operates an electrical switch 26 to turn on or off power to the heater element 18.

Figure 3 illustrates the principles of temperature control of water in the outlet 19 of the instantaneous water heater of the present invention. Water is directed from 20 aninlet 80 (downstream of the on/off valve 20) via conduits 100 to a first flow regulator 120 and a second flow regulator 130. Water which flows through the first flow regulator 120 enters the heat exchanger 14 where the water is heated with heater elements 18 as illustrated in Figure 2.

Water which flows through the second flow regulator 130 is mixed with 25 water output by the heat exchanger 14 at a mixer portion 140 without going through the heat exchanger 14. The second flow regulator 130 controls flow of water through the so-called by-pass channel 138 between the second flow regulator 130 and the mixer portion 140. The heated water from the heat exchanger 14 and the cold water from the by-pass channel 138 are mixed at mixer portion 140 and are then output 30 from the instantaneous water heater at outlet l9.

-5 From Figure 3, it will be apparent that for a given power input into the heat exchanger 14 the rise in temperature of water between the inlet 80 and the outlet 19 can be changed either by (i) varying the flow rate through the first flow regulator 120 or by (ii) varying the flow of water through the second flow regulator 130. In 5 method (i), increasing the flow through the first flow regulator 120 is effective to reduce the amount of time water spends in the heat exchanger 14. Water which spends little time in the heat exchanger 14 will have its temperature increased by less than water which spends more time in the heat exchanger 14. Thus, for a given flow rate of water through the second regulator 130, increasing flow through the first flow 10 regulator 120 will lower the outlet water temperature at outlet 19 and decreasing the flow rate through the first flow regulator 120 will increase the water temperature at outlet 19.

Alternatively, keeping the flow rate of water through the first flow regulator 120 constant, as in method (ii), the temperature of water output from the heat 15 exchanger 14 will remain constant if all other variables such as power to heater elements 18 are constant. Thus, varying the setting of the second flow regulator 130 will vary the temperature of mixed water at the outlet 19 as the temperature of the water at the outlet 19 will be equal to the fraction of water from the heat exchanger 14 multiplied by its temperature plus the fraction of water from the second flow 20 regulator l 30 multiplied by its temperature. if the flow rate of water through the second flow regulator 130 is increased, the water temperature at outlet 19 will decrease. Lowering the flow rate through the second flow regulator 130 results in an increased output water temperature.

The present invention takes advantage of these two methods of controlling 25 the water temperature at the outlet 19 to compensate for variations in the temperature of the water at inlet 80. This is achieved by varying the flow rate of water through one of the first or second flow regulators according to the temperature of water somewhere in the instantaneous water heater, preferably between the inlet 80 and the mixer portion 140. Depending upon which of the flow regulators 120, 130 is 30 controlled and where the temperature is measured different effects can be achieved.

In order to avoid the need for accounting for positive feed-back in the compensation

-6 method, the temperature sensor used to control the flow regulator should preferably not be positioned on the outlet side of the mixer portion 140.

In a first embodiment? as illustrated in Figure 4, the present invention is used in such a way as to prevent the temperature of water at the outlet 19 from rising 5 above a predetermined level. This could happen, for example, as a result of an increase in temperature of water at the inlet 80 or because of a power fluctuation resulting in the heat exchanger 14 heating the water more than usual. In the embodiment illustrated in Figure 4 the amount of water flow through the second flow regulator 130 is controlled in dependence upon the temperature of water in a 10 temperature sensing section 1 16 located in a water flow path between the heat exchanger 14 and the mixer portion 140.

The first flow regulator 120 is controlled by the user and is the main temperature selector. By increasing the rate of flow of water through the first flow regulator 120 and thereby through the heat exchanger 14 the temperature of water at 15 the outlet 19 is decreased. Conversely, decreasing the rate of flow of water through the first flow regulator 120 and thereby through the heat exchanger 14 increases the temperature of water at the outlet 1 19. In normal operation no water flow through the second flow regulator 130 is permitted. Thus, in normal operation the temperature of water at the measuring section 1 16 is substantially the same as the 20 temperature of water at the outlet 19.

If the temperature in the temperature sensing section 1 16 rises above a predetermined maximum temperature (chosen, for example, to prevent scalding) as a result of either an increase in water inlet temperature, as a result of user error in adjusting the first flow regulator 120 beyond sensible limits or due to a power surge 25 in power to the elements 18 in the heat exchanger 14, the second flow regulator 130 is partially opened. When the second flow regulator 130 is partially opened, water is allowed to flow from the inlet 80 through the by-pass 138 to the mixer portion 140.

As this water is unheated, it serves to mix with the hot water from the heat exchanger 14 thereby to reduce the temperature of water exiting at outlet 19. The amount of 30 flow allowed through the second flow regulator 130 is dependent upon the amount by which the temperature of water in the temperature sensing section l 16 has

-7 exceeded the predetermined threshold. Thus, by however much the temperature of water in the sensing section 116 exceeds the predetermined threshold, the temperature at the outlet 19 can be controlled to be equal to the predetermined threshold temperature.

5 Now the construction of the water heater the first embodiment will be described in detail. Each of the first and second flow regulators 120, 130 comprises an axially moveable member or "core" 124, 134 surrounded by an o-ring 122, 132.

The cores 124, 134 are preferably cone-like or cylindrically shaped but may be other shapes. Axially extending longitudinal grooves 126, 136 are provided on the 10 peripheral surface of the cores. The grooves 126, 136 have cross sectional areas which vary along their length. Water flows through the grooves between the cores 124, 134 and the o-rings 122, 132, the cross-sectional area of the grooves at the o ring determining the flow rate of water. By moving the cores longitudinally through the o- rings, the cross sectional area of the longitudinal grooves at the o-ring and thus 15 the flow rate of water through the flow regulator is varied. Of course, if the cores are cone-shaped less longitudinal movement of the cores in the longitudinal direction of the o-rings is required for a change in flow rate of water through the flow regulator as water can flow between the core and the o-ring at positions not occupied by the grooves 126, 136.

20 The o-rings 122, 132 could also be ofthe type which vary their diameter according to the pressure of water on the high pressure side of the associated flow regulator. Thus, the flow regulators themselves can be used to compensate for variations in pressure of water at inlet 80 thereby allowing a flow rate of water through the device dependent on the position of the core and independent of 25 variations in water pressure on the inlet side.

In the illustrated embodiment, the position of the first flow regulator 120 is manually controlled. Of course the control of the first regulator 120 could be provided by electronic means.

The position of the second flow regulator 130 is determined by the 30 temperature of water in the water temperature sensing section 116 in the following way. A temperature sensing member 118 made of a material which has an

-8 elongation which is sensitive to surrounding water temperature is mounted in the temperature sensing section 1 16. A mechanical link extending between the temperature sensing member 118 and the core 134 of the second flow regulator 130, which may be pivoted at pivot 1 17 to increase mechanical advantage, is effective to 5 vary the longitudinal displacement of the core 134 in the o-ring 132 on change in temperature and therefore elongation of element 1 18. The temperature sensing element 118 may, for example, be a wax capsule.

Alternatively, other temperature sensitive members, such as bimetallic strips, may be used.

10 It will be appreciated that the design of the second flow regulator 130 may be different to the one described above and illustrated in Figure 4. The temperature sensing arrangement may also be different. For example, the temperature sensing arrangement could be an electronic temperature sensing arrangement whereby a thermistor is placed in the temperature sensing section 1 16 and suitable control 15 electronics drive a motor or solenoid to vary the displacement of the core 134 relative to the o-ring 132 of the second flow regulator 130.

Figure 5 illustrates a second embodiment of the present invention which allows thermostatic control of the instantaneous water heater so that variations in temperature of water at inlet 80 and variations in power delivered to heat exchanger 20 114 are automatically compensated for. Thus, for a given user selected temperature, the temperature of water output at outlet 19 is constant regardless of variations in temperature of input water and of power delivered to heat exchanger 14.

The second embodiment is the same as the first embodiment except that the temperature sensing element 118 is used to drive the first flow regulator 120 rather 25 than the second flow regulator 130. The principle of operation is that heated water which exits the heat exchanger 14 should be at a constant temperature regardless of temperature of water input into the heat exchanger, of pressure of water input into the heat exchanger and of power of heat exchanger. Thus, the flow of water through the by-pass 138 selected by control of the second flow regulator 130 will be effective to 30 regulate the temperature of water at outlet 119.

In the second embodiment, there is thus partial compensation for changes in inlet water temperature and heat exchanger power (of course the temperature of water in by-pass 138 changes if the input water temperature changes). A further advantage is that there is a fast response to user demand changes and the system is particularly 5 stable.

The temperature sensing section 1 16 could be positioned elsewhere in the instantaneous water heater. For example, the temperature sensor could be positioned upstream of the heat exchanger 14. Such a system would not compensate for power variation of the heat exchanger 14 but would still compensate for temperature 10 differences in water inlet. The temperature sensing section 1 16 could even be positioned in the by-pass 138.

With electronic compensation, the temperature sensor can be placed anywhere in the flow path for water between the inlet 80 and the outlet 19. If the sensor is placed after the mixer portion 140, the electronic controller will need to 15 have information about the user, selected water output temperature.

Figure 6 illustrates a commercial embodiment of the instantaneous water heater of Figure 4. Figure 6 is best considered in conjunction Figure 2 and Figure 4.

Figure 6 does not illustrate the first flow regulator 120 but does illustrate the second flow regulator 130. As can be seen from Figure 4, the first flow regulator 120 20 controls the flow of water into the heat exchanger 14. The water flows in the heat exchanger 14 along the outside of chimney 16 through the heater elements 18. Water then enters the chimney 16 at a top end (as illustrated) and flows through the chimney 16 towards the outlet 19. It can be seen from Figure 6 that the second flow regulator 130 is attached to the chimney 16 on a bottom side thereof. The 25 temperature sensing element 1 18 is mounted at the top of the chimney 16. Two alternatives for sensing temperature are shown in the Figure, one with a single temperature sensing element and one with two separate temperature sensing elements. Two temperature sensing elements can be used if the expansion and contraction of one temperature sensing element 118 does not produce enough force 30 to move the core of the second flow regulator 130.

-10 A dividing member 139 is positioned inside the chimney 16 to separate the mixer portion 140 inside the chimney from the heat exchanger 14. The dividing member 139 is designed such that the temperature sensing element 118 is separated from the unheated water which passes through the second flow regulator 130 into the S bottom (as illustrated) of the chimney. The separating means 139 is shaped such that heated water which passes to the left hand side of it (as illustrated) is forced to mix with unheated water from the second flow regulator 130 in the mixer portion 140 in the chimney 16.

The overall arrangement can more easily be seen from Figure 7 which is a 10 cross section through the heat exchanger 14 and chimney 16 of Figures 2 and 6.

Arrows in the Figure are labelled according to the state of the water as follows: "I" indicates input water, "H" indicates water which has passed through the first flow regulator 120 and is being heated, "BP" indicates water which has passed through the second flow regulator 130 and is passing through by-pass 138 and "M" indicates I S water which is being or which has been mixed in the mixer portion 140.

First the first flow regulator 120 will be described in detail. This flow regulator has been optimised for low resistance to adjustment. First and second o rings 122a, 122b define respectively first and second orifices on their inner sides.

Positioned in the first and second orifices are first and second moveable members 20 124a, 124b (i.e. cores). The cores 122a, 122b have crosssections which generally match the inner cross-sections of the respective inner sides of the o-rings. The outer surfaces of the cores are formed with a plurality of longitudinal grooves 126a, 126b which extend longitudinally in the direction of travel of the cores and which vary in cross section along their longitudinal length. The cross-section of the longitudinal 25 grooves 126a, 126b on the first and second coresl24, 124b varies in opposite directions. On the first moveable member 124a, the longitudinal grooves 126a increase in cross-sectional area in the direction from the inlet 80 to the heat exchanger 14. On the second moveable member 124b, the longitudinal grooves 126b decrease in crosssectional area in the direction from the inlet 80 to the heat 30 exchanger 14.

-11 Movement of the first moveable member 124a towards the inlet 80 (i.e. upstream or towards the high pressure side) will increase the crosssectional area available for water to flow between the first core 124a and the first o-ring 122a. In this way more water will flow between the first o-ring 122a and the first core 124a.

5 Conversely, movement of the second moveable member towards the inlet 80 (i.e. upstream or towards the high pressure side) has the effect of decreasing the flow rate of water between the second o-ring 122b and the second core 126b.

Moving either of the moveable members 1-24a, 124b towards the inlet 80 (i. e. upstream) requires a larger force than moving them away from the inlet 80 (i.e. 10 downstream). This is because the upstream water pressure is higher than the downstream water pressure. By arranging for the first and second moveable members 124a, 124b to move in opposite directions relative to the inlet 80 and hence the flow of water i.e. by coupling them together, the force required to vary the flow rate of water through the flow regulator 120 is much reduced. Thus, as illustrated, 15 the first and second moveable members 124a, 124b are coupled such that movement of one of the moveable members 124a, 124b in a first direction in the water flow path relative to the inlet 80 causes the other of the moveable members 124a, 124b to move in a second direction in the water flow path relative to the inlet 80, the first and second directions being opposite.

20 The coupling provided in the first flow regulator 120 includes first and second racks 127a, 127b attached to the first and second moveable members 124a, 124b respectively. A pinion 128 is coupled with both the first and second racks 127a, 127b. It is effective to co-operate with the first and second racks 127a, 127b such that rotation of the pinion 128 results in movement of the first and second 25 moveable members 127a, 127b in opposite directions relative to the inlet 80.

The second flow regulator 130 works on a similar principle in that the first and second moveable members 134a, 134b are moved in opposite directions relative to the flow of water passing the moveable members. This results in a low force requirement for movement of the core as described above and so allows a wax 30 capsule 118 to be used to adjust the position of the flow regulator 130. The

-12 finctionality of the second flow regulator 130 is the same as that of the first flow regulator 120 save as described below.

In the second flow regulator 130, the first and second moveable members 134a, 134b are part of the same member and, hence, may be formed integrally. The 5 moveable member 134 is tubular and the inside 135 of the member 134 forms part of a flow path for water. First and second o- rings 132a, 132b are associated with each of the first and second moveable members 134a, 134b. Water flows from the inlet 80 through the gap between the first moveable member 134a and the first o-ring 132a to an outlet 133 positioned at the periphery of the moveable member. The outlet may 10 be at least partly annular as illustrated in Figure 6. Water also flows from the inlet 80, through the inside 135 ofthe member 134 and is then diverted to flow between the second moveable member 134b and the second o-ring 134b. Thus, if the moveable member is moved longitudinally in the o-rings 132a, 132b, the first and second moveable members 134a, 134b move in opposite directions relative to the 15 flow of water past them. As the grooves in the moveable members 134a, 134b change cross-sectional area in the same physical direction, the second regulator 130 works in a similar way to the first regulator 120 to minimise the force required to adjust the flow rate of water through the regulator.

Now the functioning of the embodiment will be described with reference to 20 Figure 7. Water from the input 80 is allowed to flow through the first flow regulator 120. The amount of water allowed to flow the first flow regulator 120 is selected by the user by rotation of pinion 128. As the water passes through the heat exchanger 14 it is heated by heating elements 18. As the heated water passes into the chimney 16 its temperature is sensed by temperature sensing element 118. If the temperature 25 is not above a predetermined maximum temperature, the heated water will pass through the mixer portion 140 to the outlet 19 without being mixed with any water from the by-pass 138. This is because the second flow regulator 130 is in a position which allows no flow of water through it.

The user may select the required temperature by varying the position of the 30 first flow regulator 120. If however, for some reason, the temperature of heated water entering the chimney 16 exceeds the predetermined maximum, the temperature

-13 sensing element 118 will expand and thereby open second flow regulator 130. Thus, unheated water flowing through the second regulator 130 will flow into the by-pass 138 and be directed by separation member 139 to the mixer portion 140 where it will be mixed with the heated water. Thus, the temperature of the water at the outlet 19 5 will be reduced to the predetermined maximum allowable. In this way, the instantaneous water heater ensures that the temperature of water at the outlet 19 does not exceed a predetermined maximum threshold temperature.

Although the present invention has been described with reference to somespecific embodiments, it is to be understood that these embodiments are given 10 merely to illustrate the principles and applications of the invention but that modifications and variations may be devised.

Claims (1)

1. -14 CLAIMS

   1. An instantaneous water heater comprising: an inlet; 5 a heat exchanger for heating water; a first flow regulator for regulating the flow of water supplied to said heat exchanger from said inlet; a mixer portion for mixing water heated by said water heater with unheated water from said inlet; and l O a second flow regulator for regulating the flow, to said mixing portion, of said unheated water from said inlet; wherein the water flow rate through one of said first or second flow regulators is automatically controlled according to the temperature of water at a predetermined position in said water heater thereby to compensate for variations in the temperature l 5 of water at said inlet.

   2. An instantaneous water heater according to claim 1, wherein said predetermined position is upstream of said mixer portion.

   20 3. An instantaneous water heater according to claim l or 2, wherein the other of said first or second flow regulators is adapted for user control to vary the flow of water through it and thereby vary the temperature of water output from said water heater.

   25 4. An instantaneous water heater according to claim l, 2 or 3, wherein said predetermined position is between said inlet and said first and/or second flow regulators. 5. An instantaneous water heater according to claim l, 2 or 3, wherein 30 said predetermined position is after said heat exchanger and before said mixer portion.

   -15 6. An instantaneous water heater according to any one of the preceding claims, wherein said one of said first or second flow regulators is mechanically controlled by a temperature-sensitive member at said predetermined position, said temperature-sensitive member having an elongation which is dependent upon 5 surrounding water temperature.

   7. An instantaneous water heater according to claim 6' wherein said temperature-sensitive member is a wax capsule.

   10 8. An instantaneous water heater according to any one of the preceding claims, wherein said one of said first or second flow regulators is said first flow regulator and the temperature of water exiting said mixer portion is substantially determined by the flow rate of water through said second flow regulator irrespective of the temperature of water at said inlet.

   9. An instantaneous water heater according to any one of claims 1 to 7, wherein said one of said first or second flow regulators is said second flow regulator and if the temperature of water exiting said heat exchanger exceeds a predetermined maximum, the flow rate of water through said second flow regulator is adjusted such 20 that the temperature of water exiting said mixer portion is at or below said predetermined maximum.

   1 O. An instantaneous water heater according to any one of the preceding claims, wherein said one of said first or second flow regulators comprises: 25 first and second movable members in first and second orifices for the flow of water therethrough, said first and second movable members being coupled such that, on actuation, they move in opposite directions relative to the flow of water through said orifices, actuation of said movable members being effective to vary the flow rate of water through said flow regulator. i

   -16 11. An instantaneous water heater according to any one of the preceding claims, wherein said first and second movable members are part of the same member and wherein said first and second movable members are hollow.

   5 12. An instantaneous water heater according to any one of the preceding claims, wherein said heat exchanger comprises: a chamber having an inlet and an outlet, the inlet being attached to an output of said first flow regulator; and heating elements positioned in said chamber for heating water flowing from 10 said inlet of said chamber to said outlet of said chamber.

   13. An instantaneous water heater according to claim 12, further comprising a chimney positioned in said chamber defining at one end said output of said heat exchanger and at another end an outlet of said water heater.

   14. An instantaneous water heater according to claim 13, wherein said mixer portion is in said chimney.

   15. A method of controlling an instantaneous water heater having an inlet, 20 a heat exchanger for heating water, a first flow regulator for regulating the flow of water supplied to said heat exchanger from said inlet, a mixer portion for mixing water heated by said water heater with unheated water from said input, and a second flow regulator for regulating the flow, to said mixing portion, of said unheated water from said inlet, said method comprising: 25 adjusting the flow rate of water through one of said first or second flow regulators according to the temperature of water at a predetermined position in said water heater thereby to compensate for variations in the temperature of water at said inlet. 30 16. An instantaneous water heater substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

   -17 17. A method of controlling an instantaneous water heater substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.