AU5174599A

AU5174599A - Water heater having multi-parameter control

Info

Publication number: AU5174599A
Application number: AU51745/99A
Authority: AU
Inventors: Alan Clarke
Original assignee: Baxi Heating UK Ltd
Current assignee: Baxi Heating UK Ltd
Priority date: 1998-07-28
Filing date: 1999-07-28
Publication date: 2000-02-21
Anticipated expiration: 2019-07-28
Also published as: WO2000006956A2; AU747152B2; EP1144919A3; ATE267368T1; GB2340213A; NZ510100A; DE69917488D1; EP1144919B1; EP1144919A2; GB9917651D0; WO2000006956A3

Abstract

A water heater (10) has a vessel (11) for holding water to be heated, a heating element (12), at least one temperature sensor (21, 22), one or more level sensors (19, 20) and a control circuit (15). The water heater (10) includes a water conditioner (23) which is operable via the control circuit (15) to prevent or reduce the precipitation of limescale from the water. This is to reduce limescale build-up within the heater, thereby increasing its efficiency and prolonging its useful life. The water is conditioned by generating a conditioning signal in the water, the conditioning signal being varied in frequency and optionally varied in intensity for greater volumes of water to be conditioned.

Description

WO 00/06956 PCT/GB99/02253 WATER HEATER HAVING MULTI-PARAMETER CONTROL Field of the Invention The present invention relates to water heaters, particularly to those commonly 10 known as vented water heaters. More particularly, the invention relates to control of parameters such as water temperature, water level and limescale precipitation. Background to the Invention Water heaters typically incorporate a vent either to allow surplus liquid to run off or to prevent excess vapour pressure from the heated water causing the vessel 15 holding the water to rupture. Conventional vented and non-vented heaters are furnished with means to control two parameters, namely the water level within a vessel for containing the water to be heated and the temperature of that water. By implementing control over these parameters, water heaters can be provided from which small quantities of hot water can be removed at irregular intervals, for 20 example, to prepare beverages. Replacement cold water is subsequently admitted to restore the level to its desired position but alters the temperature of the water in the vessel. Heating is then applied to counteract the cooling effect of the introduced cold water, to restore the temperature to a predetermined value. Mechanical control of the level can be achieved using various means such as a 25 float operated valve. Electro-mechanical means such as a rod, capillary or bimetallic disk type thermostat may be used for level and temperature control. More recently, electronic circuits controlling, via suitable electronic sensing devices, the temperature, water level or both are used.

WO 00/06956 PCT/GB99/02253 -2 Conventional water heaters suffer from a further drawback in that heating of the water will cause precipitation of limescale (principally calcium carbonate), particularly onto the water heating element. With time this can lead not only to cloudiness of the water-as the precipitate breaks free into the bulk of the liquid 5 but also heating efficiency is reduced. In order to reduce this, a number of methods have been attempted to remove or alter the chemical species involved in limescale before they enter the heater. For example, water softeners which remove ions such as calcium have been employed. These are not however suitable for drinking water applications. Sequestrants such as polyphosphates can also be 10 used, although here care must be taken not to change the character of the water, by altering for example the acidity. Furthermore, magnetic conditioners, electronic conditioners and electrolytic conditioners have also been employed. In the case of these latter three devices, the water is not "softened", the hardness salts are modified to reduce precipitation and adhesion to the internal hot surfaces of the 15 heater and pipes. To produce a single integrated water heater comprising a level and temperature control and has limescale control which can be installed safely in any location having a water and power supply, has not been achieved heretofore. The present invention has as its object, the provision of such a water heater. The object of the present invention is to provide an improved water heater which 20 includes both level and temperature control of water held in a heating vessel for subsequent dispensing. To maintain the efficiency of the heater, prevention or reduction of limescale build-up within the heater is required. It is thus the preferred object of the invention to provide a water heater having an integral limescale reducing means without adding significantly to the cost, size or 25 weight of the preferably compact heater. It is further an object of the invention to realise a water heater having integral limescale reducing means without altering the water chemically, so that palatable water for beverages is available.

WO 00/06956 PCT/GB99/02253 -3 Summary of the Invention Accordingly, the present invention provides a water heater having a vessel for holding water to be heated, a heating element, at least one temperature sensor, one or more level sensors and a control circuit, wherein the water heater includes 5 means for conditioning water to be heated, said means being operable via the control circuit, to prevent or reduce the precipitation of limescale from the water, so as to reduce limescale build-up within the heater, thereby increasing its efficiency and prolonging its useful life. The means for conditioning water comprises an induction coil or closed loop 10 antennae coiled about a water inlet pipe, the water being conditioned by inducing a conditioning signal in the water. Preferably, the conditioning signal comprises electromagnetic energy, the frequency and intensity of which is variable. The electromagnetic energy alters the characteristics of "hard water" to reduce 15 scale precipitation from the water and accumulation of that scale on hot surfaces within the heater. Preferably, the conditioning signal is intensified for greater volumes of water drawn through the inlet pipe. The conditioning signal generated cyclically sweeps through a range of 20 frequencies. The frequency sweep is non-continuous in that pre-selected frequencies are applied to the water for longer periods than other frequencies. The control circuit is housed within the water heater and includes means for correlating level and temperature signals so as to maintain substantially a pre selected volume of water at a predetermined temperature. Release of water from 25 the heater may be restricted until the predetermined temperature is achieved. Conveniently, the control circuit is governed by a microprocessor which reads sensor signals from the level and temperature sensors to control parameters of WO 00/06956 PCT/GB99/02253 -4 temperature and level within the heater. When fresh water is introduced into the heater from the inlet pipe the conditioning means is enabled. A preferred embodiment of water heater has a vessel for holding water to be heated, a heating element, a first temperature sensor located adjacent the heating 5 element, a second temperature sensor at or towards the top of the vessel to detect steam, a "half-full" level sensor, a "full" level sensor and a control circuit wherein the water heater includes a coil or antenna connected to the control circuit which induces through the loop or antenna a conditioning signal in water drawn through an inlet pipe, the conditioning signal preventing or reducing the precipitation of 10 limescale from the water. Brief Description of the Drawings The invention will now be described more particularly with reference to the accompanying drawings which show, by way of example only, one embodiment of a water heater having multi-parameter control. In the drawings: 15 Figure 1 is a schematic representation of the water heater; and Figure 2 is a schematic circuit diagram of a control circuit in accordance with the invention. Description of the Preferred Embodiment Figure 1 shows a heater, generally referenced 10, comprising a vessel 11 in which 20 water is heated by a heating element 12. The vessel is connected by inlet pipe 13 to a water supply. Control of the rate of inflow of water is by means of inlet solenoid valve 14 which is governed by the control circuit 15. The heater 10 also comprises an outlet pipe 16, allowing heated water to be drawn off to prepare beverages and through which flow is manually regulated by means of outlet valve 25 17. The vessel 11 further comprises a vent 18 through which excess pressure created by the increasing vapour pressure of the water as it is heated, is released. A level sensor 19 detects when the water level has reached a certain predetermined height and when it has, causes the inlet solenoid valve 14 to close WO 00/06956 PCT/GB99/02253 -5 off the water inlet pipe 13. A further sensor 20, is positioned to detect whether vessel 11 is less than half full. In such a situation it causes, via the control circuit 15, the heating element 12 to be switched off In this way, the risk of over heating the element 12, due to an insufficient volume of water being present is reduced. 5 The heating element 12 is further controlled by means of the temperature control sensor 21, which operates such that when the water temperature drops below a pre-set level, the element 12 is activated. Similarly when the temperature exceeds a further pre-set level then power to the element 12 is switched off, thus causing the water temperature to fall. Boiling of the water is detected by steam thermistor 10 22, which is positioned above the maximum pre-set water level and which measures the temperature of the vapour above the water. The circuit is also equipped with a boil interval timer such that, should heating not occur for a defined period, a boil sequence is initiated. The control circuit 15 may also be designed such that the power supply to the 15 heating element is varied as a function of the difference between two pre-set temperature levels, and additionally or alternatively to take into account the rate of heating for a given value of power supplied. Such a facility would be able to maintain a relatively constant water temperature and also optimise power consumption. 20 The heater 10 further comprises a closed loop antennae 23 which imparts to the water being admitted to the vessel 11 by inlet point 13, electromagnetic radiation generated in circuit 15. Such electromagnetic radiation can reduce deposition of limescale (chiefly calcium carbonate), particularly around heating elements, by altering the solution characteristics of the dissolved salts such that precipitation is 25 reduced. Typical frequencies generated by the circuit 15 to prevent scaling, all with a 50% duty cycle, are 1.5, 2.0, 2.5, 3.0, and 4.0 kHz. In use this range of frequencies sweeps sequentially backwards and forwards at a rate of approximately 16 milliseconds per frequency. Operation of the frequency generator can take place 30 either permanently, whilst the heater is in operation, or when the inlet solenoid WO 00/06956 PCT/GB99/02253 -6 valve is open. The circuit is further equipped to deactivate the frequency generation should a critical fault occur. The heater can also be provided with a start up sequence of events. In this 5 sequence, water is admitted via inlet pipe 13. Once the water level has reached the half way sensor 20, the heater element 12, is activated along with a light-emitting diode (LED) display to indicate this to the user. The inflow of water is continued until the full level sensor 19 is activated, causing the inlet solenoid valve 14 to be closed. Once the water temperature has reached a pre-set idle value, often 88C, 10 then a boil timer is initiated. Should the water then reach a temperature just below the boiling point within a certain pre-set time, the circuit 15 will cause the power to the heating element 12 to be switched off Furthermore, once the water has reached a temperature close to boiling point, the steam thermistor 22 assesses the steam temperature. Once this sensor detects a rapid rise in the steam temperature, 15 this is taken as an indication that the water is boiling and the heating element is then switched off. Once the boil time has expired, the water thermistor is calibrated. Calibration provides data for both normal and standby operation. On completion of the above stages, the commissioning sequence is then at an end, 20 and the water heater enters its idle stage. An LED display then indicates to the user that the water is ready to be drawn off Typically, the circuit will be designed such that until the heater has undergone this commissioning sequence, the indicator will not be illuminated. In normal usage, the light will be on when the temperature of the water is above the minimum usable temperature of 92C. 25 Should the water temperature drop below the pre-set value, normally 98C+/-1C, at which the temperature is to be maintained, then the circuit 15 will activate the heater. Conversely, should the temperature exceed the threshold, the heater will be deactivated. Typically a small amount of hysteresis will be introduced. In this manner the heater will not be switched on and off in rapid succession.

WO 00/06956 PCT/GB99/02253 -7 The circuit 15 mounted on a printed circuit board (PCB) detects, whether water has been drawn off during a certain defined period, perhaps by means of a timer connected to the inlet solenoid valve 14. If no water has been drawn off, then the heater can enter a standby phase, in which the water temperature is maintained at 5 the calibrated or fixed standby reference. This can again be set at 98C plus or minus I C, or whatever temperature is desired or permitted by regulation. Certain safety features can also be introduced into the heater to minimise the risk of overheating of the element, or boil off of the water, and also to prevent the water being maintained at too low a temperature which can introduce health risks. 10 For example, if the half level switch is deactivated whilst the full level switch is still active, and indicating that maximum normal level of water is present, then this will result in the heater element being switched off and the inlet solenoid valve being closed, preventing further water from entering the vessel. Also, a timer can operate, to monitor the length of time that the inlet valve is open, and if 15 a pre-set time is exceeded, cause shutdown of the heater. When other faults occur, the heater can continue to function, but at a less optimum level. Such non-critical faults are indicated to the user by, for example, an LED light flashing. An example of a non-critical fault is failure to detect boiling during the commissioning sequence. In this case water temperatures are maintained using 20 non-calibrated settings. During non-critical fault conditions, boiling is terminated either by the water temperature reaching a pre-set level, or by the boil timer expiring. Referring now to Figure 2, the control circuit 15 comprises a power supply, a power circuit for the heating element and inlet solenoid valve of the water heater 25 under control of a valve drive circuit and a signal processor for reading sensor supplied signals and interpreting those signals according to pre-programmed criteria. Mains power is supplied across mains supply connectors (CN5-1, CN6-1) to a mains transformer (TX1, TT1808) via a fuse (Fl, 200mA). A varistor (R30, 30 265VRMS) is provided to protect the power supply from mains borne transients. A 12 volt ac output from the transformer (TX1) is rectified through a diode bridge (D19 to D22, 1N4007) and regulated through a circuit centred about a standard WO 00/06956 PCT/GB99/02253 -8 regulator configuration including a switching transistor (T8, BC817) and zener diode (Z2, 5V1, BZV55C) to 5 volts for the logic circuitry. On power up, the voltage across a base connected resistor (R32) causes one of a pair of Darlington coupled transistors (T9, BC847) to turn "ON" turning "OFF" the other of tilhe 5 coupled transistors (T10, BC847) and allowing an accumulating capacitor (C16) to charge from the regulator output via a series coupled resistor R34. This provides the required reset signal to the microcontroller (IC 1, 68HC705P6ACDW). A diode (D23, 1N4007) allows rapid discharge of tilhe capacitor (C16) during power-down. Smoothing capacitors (C15, C17) are 10 provided to eliminate supply ripple. The microcontroller (IC 1) performs control functions for water heating and temperature maintenance, water filling, LED status indication and water treatment. A crystal (Y1, 4MHz) and associated capacitors (Cl, C2) form part of an oscillator circuit which operates at an overall frequency of 4MHz. 15 A bank of unit status LEDs are fed through LED driver circuits and fed via a connector (CN4-12CN4-5). The LED indicators are mounted on a separate PCB and are configured to operate in common anode mode from a rectified but unregulated 12 volt feed taken from the secondary winding of the transformer (TX1). Switching of the LEDs is performed under the control of the 20 microcontroller IC1 via switching transistors (TI to T4, BC847) provided in an emitter follower configuration in the driver circuits. This configuration prevents variations in the unregulated supply from affecting the LED current and hence the intensity of the LEDs. Resistors (R19, R21, R23, R25) set the LED operating current at approximately 9mA. 25 A relay (RL1, GHP-1111P-12VDC) and its associated switching transistor (T6, BC817) control power to the heating element (via connectors CN7-1, CN8-1) again under control of the microcontroller (ICI). A snubber network (C18, R35) is formed across the relay contacts to reduce switching interference. The voltage developed across a ground connected resistor (R51) can be used by the 30 microcontroller (IC1) to measure the relay current. An optical coupler (ICS, TLP3062) and associated components (transistors T7, BC847 and T12, BC857) provide water inlet solenoid valve control. As the first WO 00/06956 PCT/GB99/02253 -9 solenoid driver transistor (T7) is turned "ON", so the second driver transistor (T12) is driven "ON" supplying current to the optical coupler IC5 allowing current to flow through to the valve connector (CNIO-1, CN9-1). A snubber network (C19, R44) is provided to help reduce switching interference. The 5 optical coupler circuit includes a detector that only allows switching to occur at the mains waveform zero crossing point. Input signals from the full and half full float switches across float signal connectors (CNI-5 and CN1-10, CN1-4 and CN1-3) are presented to the microcontroller (IC1) via series resistors (R2, R4). The active state for the float 10 switches is normally closed. In this condition, current flows to ground (GND) from optical coupler (ICS) via series resistor (R39) for the full float switch and via a resistor (R45), coupled to the 12 volt rail, for the half-full float switch. The full float switch completes the current path for the water solenoid valve optical coupler (ICS). This ensures that a failure of the microcontroller (IC1) will not 15 cause an over-fill condition. The 12 volt rail coupled resistor (R45) provides a whetting current when the half-full float switch closes. Steering diodes (D9 and D10O, IN4007) provide a path to ground (GND) via pull up resistors (R3, R5) on the full float and half-full float switch circuits, respectively. This arrangement allows the microcontroller (ICI) to detect float switch activation at a low logic 20 level (at PC0 and PC 1). The steam thermistor input is presented also across a connector (CNI-6, CN1-7) for feeding data to the microcontroller (IC1). The thermistor and a resistor (R1 1) tied to the 5 volt rail together form a potential divider to provide a control voltage to one part of a conditioning operational amplifier (IC3A, LM2904). The gain of 25 the thermistor signal is increased here and the voltage span is reduced to allow the microcontroller (ICI) to monitor (at PC5/AN1) a relatively small temperature range. The water thermistor input is taken across its respective connector (CN1-8, CN1-9) and is conditioned in an identical way to the second part of the conditioning operational amplifier (IC3B) but includes a switching transistor 30 (T1 1, BC847) in the circuit. In the present embodiment of the invention, two temperature ranges may be measured by shorting out a resistor (R43) by switching the transistor (T1 1) via the microcontroller (ICI, at PA7). Similarly, the transistor (T 1) can be turned "OFF" to provide extended water temperature coverage. The WO 00/06956 PCT/GB99/02253 -10 outputs of both parts of the conditioning operational amplifier (IC3A, IC3B) are fed via protection resistors (R48, R49) to ADC channels 0 and I (PC6/ANO, PC5/ANI) on the microcontroller (ICI). Capacitors (C7, C8, C9, C10) are provided to help increase noise immunity. 5 The water treatment driver circuitry comprises a switching transistor (TS, BC817) and associated components. A current is unlimited by a protection resistor (R27) to approximately 70mA. The driver of the circuit is controlled by the microcontroller (ICI) which generates a variable frequency square-wave output. The resulting output current flows through a wire loop provided across the 10 descaler connector (CN1-1, CNI-2) to provide conditioning of the incoming water flow. The frequency and amplitude of the electromagnetic wave induced in the wire loop is controlled by the microcontroller (IC 1, at TCMP). The microcontroller (ICI) is provided with pre-selected program instructions to read, interpret and act upon level and temperature parameters. The programming 15 includes initialisation procedures and fault condition contingencies. The overall operation of the programming is indicated below: The water heater always assumes that the tank is empty whenever the unit is powered up. If the tank is not empty but full then the inlet solenoid for valve is deactivated. 20 The following processes shall operate during the commissioning phase: * The "POWER" LED flashes until unit commissioning is complete. For water heating and water boiling the following processes are followed: * For water heat, the heater does not activate until the water level has activated the half full float switch and the steam thermistor has reached a minimum 25 temperature. This ensures that the unit cannot heat an empty tank or continue to boil if power is removed during the boil stage. A timer operates to determine the maximum time allowed for the steam and water temperatures to reach their idle states. Failure of the steam thermistor to reach an idle state WO 00/06956 PCT/GB99/02253 -11 shall be determined as a non-critical fault condition. The unit waits for the water tank thermistor to begin rising from the idle value (approx. 88 Centigrade). A timer shall operate during this period and if allowed to expire shall cause a critical fault condition. The water tank temperature is monitored 5 from the minimum setting until the temperature reaches a point just below boiling. Note, this setting can only be approximate. A rise in temperature shall be expected throughout this period with the unit entering a critical fault condition if this is not achieved. This enables correct water tank thermistor operation to be determined. If the water temperature has reached near boiling 10 point at power on the unit shall proceed to check for the steam condition. For water boil, the unit normally expects to see a rapid rise in steam temperature to indicate the start of a boiling condition. Once boiling has been detected the unit switches off the heater. Water thermistor calibration takes place after expiry of the boil timer. 15 The above event indicates the end of the initialisation sequence. The water heater enters the idle state. The ready LED illuminates indicating that the unit is ready for use. The water tank thermistor is calibrated to provide the tank temperature maintenance points for both normal and standby operation. Failure to detect boiling shall result in a non-critical fault condition being generated and 20 termination of the initialisation sequence. The normal and standby water temperatures are maintained using a non-calibrated setting. If water boils during fault condition, a boil timer shall operate during this condition. If allowed to expire the unit terminates boiling. The normal and standby water temperatures are maintained using a non-calibrated setting. Boiling 25 is terminated when the water temperature reaches a pre-set boiling point. The following processes operate during water tank filling: The tank fills from empty and when the water level has risen the required amount to activate the half full level float switch, the half full LED illuminates. The half full LED extinguishes as water is drawn from the unit below the level of the half 30 full level float switch. Activation of the full level float switch without WO 00/06956 PCT/GB99/02253 -12 corresponding activation of the half level float switch shall cause the unit to enter a critical fault condition. The water level is expected to rise and activate the full level float switch at which time the full level LED illuminates. The water inlet solenoid is immediately 5 deactivated. A boil sequence is initiated if the unit was in standby mode when water was requested. The water inlet solenoid activates when water is drawn from the unit and the full level LED extinguishes indicating that the tank in no longer full. The water boil sequence is subsequently initiated on expiry of the boil duration timer. The unit 10 enters its standby mode if no water has been drawn off for a pre-selected period of time. De-activation of the half full level float switch while the full level float switch is activated shall cause the unit to enter a critical fault condition. A water boil sequence in progress terminates when water is drawn from the unit. The unit enters normal operation when the normally active full level float switch 15 is deactivated. The water fill timer monitors all water fill activities and if allowed to expire, causes the unit to enter a critical fault condition. The timer setting is selected to be sufficiently long in duration to avoid "timing out" under normal use. On expiry of the boil interval timer the unit initiates a boil sequence. Operation is 20 similar to that used during unit commissioning with the exception that no check is made for the water level being half full. For heater control during normal operation, the water tank temperature is maintained at the calibrated or fixed working reference. A small amount of hysteresis is provided to prevent rapid heater switching. Where the water 25 thermistor has been calibrated the maintained temperature is 98 +/- 1 Centigrade. The heater is activated when the water tank temperature drops below the low threshold. The heater is deactivated when the water tank temperature rises above the high threshold.

WO 00/06956 PCT/GB99/02253 -13 For heater control during standby operation, the water tank temperature is maintained at the calibrated or fixed standby reference. A small amount of hysteresis is again provided to prevent rapid heater switching. Where the water thermistor has been calibrated the maintained temperature is 98 +/- 1 Centigrade. 5 The heater is activated when the water tank temperature drops below the low threshold. The heater is deactivated when the water tank temperature rises above the high threshold. Indications that the unit is ready for use or near ready are provided by panel front mounted LEDs. The "READY" LED does not illuminate until the unit has 10 completed the initialisation procedure. The "READY" LED illuminates when the water tank is above the minimum useable temperature of 92 and extinguishes when the water tank drops below the minimum useable temperature. Two types of system fault shall be catered for and indicated: 15 * A non-critical fault is defined as a fault which does not affect unit operation from the user's perspective but should be rectified as soon as possible. A non critical system fault is indicated by briefly flashing the "READY" LED. The indication operates in such a way as not to detract from the descale indication. If the normal state of the LED is extinguished then a fault condition shall 20 cause a regular, brief illumination. The unit shall assume that all faults have been rectified when re-powered and enters the initialisation procedure. The water conditioning circuit is active during normal unit operation but is deactivated during a critical fault condition. Where "hard" water is stored and heated a proportion of the "hardness salts" (for 25 example calcium carbonate) precipitates out of the water and adheres to hot surfaces within the water heater. This can lead to a reduction in efficiency of the heating means by effectively forming an insulating barrier of limescale on the surface of the heating means; and/or a reduction in flow performance by reducing the cross sectional bore of inlet and outlet pipes.

WO 00/06956 PCT/GB99/02253 -14 The proposed control is an electronic circuit that combines the temperature and level control functions with an electronic scale conditioning device that can be incorporated into the water heater thus obviating the need for a number of separate devices. 5 The circuit controls: temperature by means of an electronic sensing device (typically a thermistor) which provides a signal to the circuit to make or break an electrical supply to the heating means at a pre-set temperature. The sensor detects whether the water temperature is below its pre-set value. If it 10 is a switching means is enabled that provides electrical power to the heating means and hence raising the water temperature. When the sensor detects the pre set temperature has been reached the switching means is disabled thus interrupting the electrical supply to the heating means and thus preventing any further temperature rise. 15 * Water level by means of a further electronic sensing device or devices which provides a signal to the circuit when the water level within the heater reaches a predetermined level to make or break an electrical supply to a means of controlling the inlet water flow (typically a solenoid valve). If the water level within the water heater is below its "full" level the sensor 20 positioned at the "full" level will detect this and provide a signal to the control circuit. This signal will enable a switching means to provide power to a flow control device and hence allow water to enter the heater from the water supply to replenish the heater. When the "full" sensor level is reached by the water the signal to the circuit will be interrupted hence de-energising the flow control 25 device, stopping the inlet water flow and consequently any further rise in water level within the heater. A further sensor may act as a "low" level sensor to prevent the heating means being energised should the water level be at a level where the heating means was not immersed. Other sensors may be incorporated at differing levels to give signals of varying WO 00/06956 PCT/GB99/02253 -15 degrees of fill level up to the "full" level, signals from these sensors can be used to switch visual indicators (typically an LED or neon) of the level of fill achieved. SScale conditioning of the inlet water supply. A range of electromagnetic waves of varying frequency are generated within the 5 control circuitry and are imparted to the water supply by a closed loop antenna, the antenna being coiled around the inlet pipe of the water heater such that water flowing into the heater is conditioned. Application of the electromagnetic fields has been shown the alter the characteristics of the "hardness salts" such that they do not precipitate out of the water and adhere to hot surfaces within the heater. 10 The control circuitry may also include safeguards to ensure the heating means is not energised unless a predetermined water level has been achieved; user selection of differing control temperatures; other indications of water heater status e.g. mains power on, correct storage temperature has been achieved, scale conditioning is operating, etc. 15 Temperature control, level control and scale conditioning are achieved by using one control circuit rather than several discrete devices. Scale conditioning does not remove the hardness salts from the water thus retaining beneficial trace elements. Water remains suitable for drinking purposes making this type of control 20 especially suitable for use in water heaters for dispensing hot water for beverage making. Maintenance of the water heater is reduced in hard water areas due to the reduction in scale formation within the heater.

WO 00/06956 PCT/GB99/02253 -16 It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modification and alteration are possible within the scope of the appended claims.

Claims

1. A water heater (10) having a vessel (11) for holding water to be heated, a heating element (12), at least one temperature sensor (21,22), one or more level sensors (19, 20) and a control circuit (15), wherein the water heater 5 (10) includes means (23) for conditioning water to be heated, said means (23) being operable via the control circuit (15) to prevent or reduce the precipitation of limescale from the water, so as to reduce limescale build up within the heater (10), thereby increasing its efficiency and prolonging its useful life. 10

2. A water heater according to claim 1, wherein the means for conditioning water comprises an induction coil or closed loop antennae (23) coiled about a water inlet pipe (13), the water being conditioned by inducing a conditioning signal in the water.

3. A water heater according to claim 2, wherein the conditioning signal 15 comprises electromagnetic energy the frequency and intensity of which is variable.

4. A water heater according to claim 3, wherein the electromagnetic energy alters the characteristics of "hard water" to reduce scale precipitation from the water and accumulation of that scale on hot surfaces within the heater. 20

5. A water heater according to any one of claims 2 to 4, wherein the conditioning signal is intensified for greater volumes of water drawn through the inlet pipe (13).

6. A water heater according to any one of claims 2 to 5, wherein the conditioning signal generated cyclically sweeps through a range of 25 frequencies.

7. A water heater according to claim 6, wherein the frequency sweep is non continuous in that pre-selected frequencies are applied to the water for longer periods than other frequencies. WO 00/06956 PCT/GB99/02253 -18

8. A water heater according to any preceding claim, wherein the control circuit (15) is housed within the water heater and includes means for correlating level and temperature signals so as to maintain substantially a pre-selected volume of water at a predetermined temperature, release of 5 water from the heater being restricted until a predetermined temperature is achieved.

9. A water heater according to any preceding claim, wherein the control circuit is governed by a microprocessor which reads sensor signals from the level and temperature sensors to control parameters of temperature and 10 level within the heater the conditioning means being enabled when fresh water is introduced into the heater.

10. A water heater according to claim 1, wherein the water heater (10) has a vessel (11) for holding water to be heated, a heating element (12), a first temperature sensor (21) located adjacent the heating element (12), a 15 second temperature sensor (22) at or towards the top of the vessel (11) to detect steam, a "half-full" level sensor (20), a "full" level sensor (19) and a control circuit (15) wherein the water heater (10) includes a coil or antenna (23) connected to the control circuit (15) which induces through the loop or antenna (23) a conditioning signal in water drawn through an inlet pipe 20 (13), the conditioning signal preventing or reducing the precipitation of limescale from the water.

11. A water heater substantially as herein described with reference to and as shown schematically in the accompanying drawings.