Patent Publication Number: US-2011058798-A1

Title: Liquid heating apparatus

Description:
This application is entitled to the benefit of, and incorporates by reference essential subject matter disclosed in PCT Application No. PCT/GB2008/004249 filed on Dec. 23, 2008, which claims priority to Great Britain Application No. 0725235.6 filed Dec. 24, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to a liquid heating apparatus for heating/boiling liquids such as water. 
     2. Background Information 
     There is a common need almost all over the world to heat water in order to make beverages. In the UK and other parts of Europe, it is common for most households to own a kettle which is used to boil water for making occasional beverages. In larger establishments and also in other parts of the world, it is more common to keep a body of water hot or boiling for a prolonged period of time—possibly all day—in order to be able to make such beverages “on demand”, i.e. without having to wait for the water to heat up from room temperature. An example of this would be a traditional electric urn or, more commonly in Asia, a so-called airpot. 
     Both of these arrangements have their disadvantages. In the case of the kettle, the time taken for the water to heat from cold (i.e. the temperature from which it is drawn from the tap) is seen as inconvenient to users, even those using very high power kettles (of the order of 3 kilowatts). This is particularly so given the difficulty in estimating the volume of water required when the kettle is being filled and the attendant tendency to boil more water than is needed which of course increases the time taken for it to boil. On the other hand, if water is kept for a prolonged period of time either at or just below boiling, a significant amount of energy will be required to counter the unavoidable heat loss. 
     Recently, devices attempting to bridge this gap have been commercialized. These are said to be able to deliver a cupful of hot water from a reservoir of cold water within a matter of seconds. However, these devices are typically based on a tubular flow heater and the applicant has appreciated some significant drawbacks to this arrangement. Firstly, as is typical of tubular flow heaters, heating must be ceased before the water in the tube reaches boiling point in order to avoid the danger of the heater overheating through hot spots created by pockets of water vapor and/or the pressure inside the tube building up too high. Another drawback is that although the heater heats up relatively quickly, there is inevitably an initial volume of water which passes through the heater which is not heated to the target temperature. This mixes with the water produced later, itself still not at boiling point, to reduce the average temperature of the water. The combination of these two factors means that in practice the water provided by such devices is at well below boiling point by the time it is dispensed, making it unsuitable for example for making tea and thereby limiting its consumer appeal. 
     The Applicant has further appreciated that most users will still need to keep a conventional kettle in addition to a one-cup hot water dispenser of the type discussed above, for when a larger quantity of truly boiling water is needed. This creates problems in terms of space taken up in the kitchen. 
     SUMMARY OF THE DISCLOSURE 
     When viewed from a first aspect the present invention provides a liquid heating apparatus having a first mode of operation in which a first volume of water can be heated and a second mode of operation in which a second, smaller volume of water can be heated and automatically dispensed. 
     It will be seen by those skilled in the art that in accordance with the invention a single apparatus can be used either to heat and dispense a small volume of water rapidly, or to heat or boil a larger quantity of water more conventionally. This has the advantage of allowing the user to select the appropriate mode of operation according to the volume of water required at any particular time, but without the cost associated with separate appliances for these tasks or the need to find space for multiple appliances on a kitchen worktop. Of course it should be understood that the relative volumes of water that can be heated in either mode is determined by the relative maximum capacities; at least in preferred embodiments the first mode of operation could be used to heat a volume of water that is sufficiently small that it could have been heated in the second mode instead. The volume of water that can be heated in the second mode may be fixed or might be variable—e.g. by a user. 
     The apparatus could be provided with separate reservoirs for the two respective modes of operation, but in preferred embodiments a common reservoir is provided. This could be arranged to dispense water (or another liquid) to respective heating arrangements depending upon whether the first or second mode of operation was being employed, but in preferred embodiments the apparatus is arranged to heat all the water in the reservoir in the first mode of operation, or a smaller, predetermined amount of water from the reservoir in the second mode of operation. 
     The apparatus preferably comprises a removable reservoir which is advantageous in facilitating filling, since the reservoir can be removed from the rest of the apparatus and taken e.g. to a tap to fill it. In particularly convenient embodiments, the apparatus is also arranged such that water heated in the first mode of operation can be manually dispensed from the removable vessel. The removable vessel can, preferably, resemble an ordinary kettle and it will be appreciated therefore that in these embodiments the apparatus essentially comprises a standard water boiling kettle but the apparatus is also configured to be able to heat and dispense water “on demand” if the volume required is small enough. 
     A common heating means could be employed to heat water in either the first or second mode of operation. For example, a reservoir could comprise means to divide off a small volume therefrom which can be heated in the second mode of operation. In other embodiments, independent heating means are provided for the first and second mode of operation respectively. This might have some advantages in terms of optimizing each heater for its particular use and also lends itself particularly to embodiments where essentially a complete water boiling kettle is provided for operation in the first mode but which, when placed on the apparatus, allows water from the kettle to enter the heater for the second mode of operation. It will be appreciated that in such embodiments the kettle could be operated independently of the rest of the apparatus, only needing to be placed on the rest of the apparatus when the second mode of operation was required. 
     Such arrangements are novel and advantageous in their own right and thus when viewed from a further aspect the invention provides an apparatus for heating liquid comprising a removable liquid heating vessel comprising a heater for heating liquid therein, the apparatus further comprising a second heating chamber arranged to heat liquid and dispense it through an outlet, wherein said second heating chamber is filled with liquid from the removable liquid heating vessel. 
     Preferably one or both heaters are arranged to heat water to boiling. In comparison with the first aspect of the invention the removable liquid heating vessel provides the first mode of operation and the second heating chamber provides the second mode. 
     In accordance with all the aforementioned embodiments, it is preferred for the heater for heating liquid in the first mode of operation, e.g. the heater of the liquid heating vessel in the aspect of the invention set out above, to comprise a heater plate with a resistance heating element, e.g. a sheathed element, formed on or mounted to the underside of the plate. Preferably the heater is arranged to close an opening in the base of the vessel as is well-known in the art of kettles. 
     Where an independent heater for the second mode of operation is provided, e.g. the heater of the second heating chamber in the aspect of the invention set out above, this could take any convenient form, e.g. a tubular heater or some other form of flow heater, but preferably a chamber is provided in which the liquid is heated to the desired temperature and then dispensed. 
     The automatic dispensing in the second mode of operation could be effected by any suitable means. For example, a pump could be employed or the apparatus might be arranged such that the liquid is heated in an upper part thereof and dispensed lower down through hydrostatic pressure. In preferred embodiments, however, the water is arranged to be boiled in the second mode of operation and is dispensed from the apparatus with the aid of steam pressure generated during boiling. 
     In some embodiments of the invention a common mechanism is provided to cease heating of the liquid when it has reached a predetermined temperature, regardless of whether this is in the first or the second mode of operation. This could take any convenient form, e.g. electronic, and may be dependent upon the temperature to which the liquid is being heated. In preferred embodiments in which water is boiled in both modes of operation, the common means preferably comprises a steam switch, e.g. one comprising a snap acting bimetallic actuator, as is well-known in the art. 
     In other embodiments independent means are provided to cease heating in the respective modes. For example where a removable liquid heating vessel is provided, a conventional steam switch could be provided. This for example allows such a removable vessel to be as close as possible to a standard kettle which is beneficial both in terms of user acceptance and in being able to minimize re-tooling. 
     The removable liquid heating vessel preferably comprises valve means for selectively allowing liquid into the second heating chamber when the vessel is installed on the appliance and preventing leaking when it is removed. The valve means could be provided in the vessel body, but preferably it is provided in a heater plate closing an opening in the base of the vessel. This is beneficial in having the valve lowermost in the vessel but also means that a standard heater plate incorporating the valve can be produced, thereby allowing appliance manufacturers to use appliance bodies that have already been tooled. 
     Although not essential, preferably valve means are also provided on the second heating chamber. Preferably such valve means are configured to close when there is a predetermined amount of water in the second heating chamber. This allows the second heating chamber to fill automatically to the required level. It could for example comprise a float valve. In accordance with one set of embodiments, a freely floating valve member is employed, which is more robust than a flap valve. Advantageously, such a valve member is received in a housing which permits liquid flow through it but retains the valve member, the valve member having an upper position in which it is against a valve seat to close the valve and a lower position where it is retained in the lower part of the housing. The valve member might take any convenient form. For example it could comprise a ball. Alternatively it could be pill, discus or squat-cylindrical in shape. In a preferred set of embodiments the valve member is downwardly tapering, e.g. frusto-conical. This has been found to minimize the chance of the valve member sticking during use. 
     Preferably the second heating chamber valve means is configured such that increasing pressure in the heating chamber tends to increase the closure pressure on the valve arising from the buoyancy of the valve member. Preferably it comprises a resilient collar against which the valve member is pressed by internal pressure in the second heating chamber. This helps to prevent leakage of water or steam when the removable vessel is removed. 
     Where, as is preferred, separate heaters are provided for the two respective modes of operation, preferably the apparatus comprises a switching arrangement which only permits energization of one of said elements at time. This is advantageous as it allows each heater to be high power without running the risk of overloading the mains electrical supply by both being energized at once. In a simple exemplary embodiment the switching arrangement could comprise a change-over switch such as a rocker switch. Where provided the steam switch preferably acts on the aforementioned switching arrangement to switch off whichever heater is being energized. 
     The above-mentioned arrangement is considered to be novel and inventive in its own right and thus when viewed from another aspect the invention provides a switching arrangement for an electrical appliance, said switching arrangement comprising a switch having a first position in which a first circuit can be powered, a second position in which a second circuit can be powered and a third position in which neither of said circuits is powered, said arrangement further comprising a thermally responsive actuator arranged to act on said switch so as to move the switch from either of said first or second positions to said third position upon said actuator reaching a predetermined temperature. 
     In other embodiments an electronic or electro-mechanical arrangement is employed to prevent simultaneous energization. For example in one set of embodiments a relay is employed in series with the electrical supply to one of the heaters and is arranged such that the contacts thereof are opened when power is supplied to the other heater. Of course the skilled person will readily conceive of equivalent means for achieving the same function electronically. Preferably the arrangement is such as to cut off power to the removable liquid heating vessel when the heater of the second heating chamber is energized. This is beneficial in that it allows the electrical arrangement in the liquid heating vessel to be entirely standard. For example the relay or other switching arrangement could simply cut power to a cordless connector such as the Applicant&#39;s P72 connector which is used to supply power to the liquid heating vessel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic diagram showing the main parts of an apparatus embodying the invention; 
         FIG. 2  is a schematic circuit diagram illustrating the electrical switch arrangement for the two heaters; 
         FIGS. 3   a  to  3   d  are a series of schematic diagrams showing use of an embodiment of the invention; 
         FIG. 4  is a further schematic diagram of a second embodiment; 
         FIG. 5  is a perspective view of a third embodiment of the invention; 
         FIG. 6  is a perspective view, from a different angle, of the embodiment of  FIG. 5  with the jug kettle part removed; 
         FIG. 7  is a view similar to  FIG. 6  with the outer cover removed; 
         FIG. 8  is a partly exploded view of the parts above the heating chamber; 
         FIG. 9  is cross-sectional view through the heating chamber; 
         FIG. 10  is a different section through the heating chamber; 
         FIG. 11  is an enlarged sectional view of the valve between the jug kettle and the heating chamber; 
         FIG. 12  is a perspective view of the lower part of the dispensing chamber; 
         FIG. 13  is a sectional view through the dispensing chamber; and 
         FIG. 14  is schematic circuit diagram for the appliance. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the basic parts of an apparatus embodying the invention. In this embodiment there is an almost-standard jug kettle  2  having a lifting handle  4  and a pouring spout  6 . The kettle is fitted with a heater arranged to close an opening in the base thereof and comprises a sheathed heating element mounted to the underside of a metal plate. The kettle  2  also comprises the Applicant&#39;s standard U17 control unit in order to switch off the heater in the event that it overheats due to being switched on dry or boiling dry. As is well known in the art such a control unit includes the male part of a 360 degree cordless electrical connector. The female part of the connector  8  is visible on the base part of the apparatus  10 . 
     Where the kettle  2  differs from an ordinary one is that on its base it comprises a self-closing valve (not visible) which can be opened by penetration of a tube  12  protruding from the base  10  when the kettle  2  is placed on the base  10 . At the lower end of the tube  12  is another valve in the form of a float valve  13 , controlling the entry of water from the kettle  2  to a heating chamber in the base  10 . 
     The heating chamber inside the base of the apparatus  10  has another heater  30  at the underside thereof which is similar to the heater in the kettle  2 . As well as the inlet controlled by the float valve  13  as just described, the base heating chamber is connected to a dispensing spout  14  which protrudes from the base part  10  and ends with a downward loop for dispensing heated water into a cup  16  or other receptacle placed beneath it. 
     Also communicating with the heating chamber and rising from the base  10  of the apparatus is a vertical steam tube  18  with a narrow neck at its upper end, beyond which is a thermally responsive snap-acting bimetallic actuator  20 . Although not shown in the schematic representation of  FIG. 1 , the bimetal  20  is positioned such that it also lies above the spout  6  of the kettle  2  when it is positioned on the base unit  10 . 
       FIG. 2  is a schematic circuit diagram showing the switching arrangement. It will be noted from this that the bimetal  20  acts on a change-over type rocker switch  36 . The rocker switch  36  has three positions. In the left and right positions it can complete a circuit between a common terminal  22 , connected to the live side of the mains supply, and either one of two other terminals  24 ,  26 , connected respectively to the element  28  in the kettle  2  and the element  30  in the base heating chamber. In the central position of the switch  36 , neither circuit is completed. 
     This arrangement allows either element  28 ,  30  to be energized or neither to be energized, but does not physically allow both elements to be energized at the same time. Consequently each element can be at the maximum power rating for the mains supply—e.g. 3 kW in the UK. The bimetallic actuator  20 , when it reaches its operating temperature (e.g. ninety degrees C.), after coming into contact with steam, acts on the switch  36  to return it to the central, open position (depicted in  FIG. 2 ) in which neither element is energized. 
     In series with the kettle element  28  are the respective live and neutral pole switch contact sets  32  of the U17 control unit. In series with the base heating chamber element  30  are a simple bimetallic thermostatic switch and a thermal fuse switch or two bimetallic switches (not shown). These respective further switches ensure that the elements are de-energized in the event of overheating—e.g. due to being switched on dry or boiling dry. 
     Operation of the apparatus will now be described with additional reference to  FIGS. 3   a  to  3   d .  FIG. 4   a  shows the apparatus with the kettle  2  placed on the base part  10  and with a cup  16  placed beneath the dispensing spout (not visible). In use the user removes the kettle  2  from the base unit  10  and fills it from a tap in the conventional way ( FIG. 4   b ). It is then replaced on the base part  10 , thereby allowing the tube  12  to penetrate the bottom of the kettle and to allow water to be drawn out from it subject to the float valve  13  being open (i.e. if the base heating chamber is empty). 
     In a first mode of operation a user can boil a relatively large volume of water (e.g. up to two liters). This is done by selecting the appropriate position for the rocker switch  36 . This energizes the kettle element  28  so that it boils the whole contents of the kettle  2 . When the water has boiled, the steam produced will cause the bimetal  20  to operate which in returns the rocker switch  36  to the central, off position which interrupts power to the cordless connector  8  and so de-energizes the element  28  in the kettle. Of course, instead of this arrangement a more conventional steam switch arrangement could be employed in the kettle  2  itself. With a 3 kW heating element it would take approximately 4 minutes to boil two liters of water. Once the element has been switched off after the water has boiled, the kettle  2  can be picked up and the water poured out in the normal way ( FIG. 3   c ). 
     If instead the user requires only a cupful of boiling water, a second mode of operation can be employed. This is done by selecting the other position of the rocker switch  36  ( FIG. 3   d ) and thereby energizing the in the base chamber heater  30 . 
     This rapidly heats the small volume of water in the chamber to boiling, with the steam thereby produced entering the steam tube  18  and actuating the bimetal  20  and returning the switch  36  to the central position so switching off the element. The increase in pressure associated with the water in the chamber being boiled forces it up through the dispensing spout  14  and into the cup  16 . A cupful of water can be boiled and dispensed in approximately 30 seconds. 
       FIG. 4  shows schematically a further embodiment. This has a similar arrangement of a removable kettle  2 ′ with its own element (not shown) and a side-entry water feed tube  12 ′ for drawing water from the kettle  2 ′ for rapidly heating and automatically dispensing a small, predetermined body of water through the spout  14 ′ to the cup  16 . In this embodiment however, instead of a heater on the underside of an enclosed base heating chamber, there is a flow heater  30 ′ for heating the water for the second mode of operation. 
     Thus it will be appreciated by those skilled in the art that the embodiment described above allows a user the flexibility to be able to boil a cupful of water very rapidly, or to boil a kettle full of water in the usual way, but without having to buy, and find storage space for, two separate appliances. 
     The embodiment described is merely one example of how the invention can be implemented. Many variations and modifications can be made. For example rather than having two separate heating elements for the two modes of operation, a single common element could be provided. 
       FIG. 5  shows a perspective view of a further embodiment of the invention. This broadly comprises a removable liquid heating vessel in the form of a jug kettle  40  which is placed on a stand  42  which also serves to support a hot water dispensing chamber  44  with its dispensing spout  45  by means of a pillar  46 . The kettle  40  is shown with the lid and outer handle molding removed. This reveals a standard steam switch  48  such as the applicant&#39;s R48 steam control which is used to switch the kettle off when water inside it boils. 
       FIG. 6  shows the apparatus with the kettle removed. This reveals a 360° cordless electrical connector  50  such as the applicant&#39;s P72 connector located centrally within the region of the base  42  which receives the kettle. To one side of the cordless electrical connector  50  is the outer housing of water valve  52 , the purpose of which will be described later. 
     Also more easily visible in this drawing is the on/off switch  54  on top of the hot water dispensing chamber  44  and the drip tray  56  which is directly beneath the spout  45  (not shown in  FIG. 6 ). 
       FIG. 7  shows a view of the main parts of the appliance with the outer covers removed. Thus in the lower part of the appliance there can now be seen a heating chamber  58  with which the valve  52  selectively communicates. Extending from the side of the heating chamber  58  are two tubes  60 ,  62  which connect the interior of the heating chamber  58  to the interior of the dispensing chamber  44 . The purpose of these two tubes will be described later. 
       FIG. 8  shows a partially exploded view of the parts above the heating chamber. This shows that the 360° cordless connector  50  is received in a special recess  60  in the top face of the heating chamber  58 . A channel  62  is provided to accommodate the wires coming from the connector  50 . The connector  50  is held in place by a plate  64  which is screwed, riveted or otherwise attached to the top of the heating chamber  58 . The securing plate  64  also provides the outer valve housing  52 . The outer valve  52  housing fits over an upstanding annular wall  66  on the top of the heating chamber with a novel resilient annular sealing member  68 , which will be described in more detail later, interposed between them. 
     The heating chamber  58  is formed from upper and lower parts which are clamped together by clamp rings  70 ,  72  which are screwed together by a series of boss and screw arrangements  74 . 
       FIG. 9  shows a vertical cross-section through the heating chamber  58 . From this figure can be seen the sheathed resistance heating element  76  bonded to an aluminum diffuser plate  78  which is in turn bonded to the underside of a stainless steel heater plate  80 , the foregoing construction being similar to that conventionally used in water-boiling kettles. The heater plate  80  is attached to the upper body of the heating chamber  58  by means of a peripheral channel  82  which is crimped over a downwardly depending wall portion of the heating chamber in accordance with the applicant&#39;s Sure Seal system which is described in greater detail in WO 96/18331. 
     Also visible in this figure is a section through one of the tubes  60  connecting the heating chamber  58  to the dispensing chamber (not shown). This is the outlet tube for conveying boiling water from the heating chamber  58  to the dispensing chamber. It will be apparent from the Figure that inside the chamber the outlet tube  60  extends in a right angle arrangement to terminate in a downwardly depending tube portion  84 , the end of which is a few millimeters above the heater plate  80 . 
       FIG. 10  also shows a vertical cross-section through the heating chamber  58 , although in this instance the section is taken through a plane parallel to that of  FIG. 9 . This shows the other tube  62  connecting the heating chamber  58  to the dispensing chamber which is a vent tube. The lower end of the vent tube  62  fits over a spigot  86  which opens into a hole at the top of the interior of the heating chamber  58 . 
       FIG. 11  shows a vertical cross-section through the kettle  40  seated on top of the heating chamber  58 . In this figure, the view has been enlarged to show the valve arrangement more clearly and some components have been omitted to enhance clarity further. The kettle  40  has a side wall  88 . The underside of the kettle is closed by a circular stainless steel heating plate  90 , on the underside of which is provided an aluminum diffuser plate  92  and a sheathed resistance heating element (not visible). 
     A hole is formed towards the edge of the heater plate  90  to accommodate the vertically protruding spigot portion  94  of the kettle part of the valve mechanism. This spigot portion  94  is sealed against the hole in the heater plate  90  by means of a grommet  96 . Beneath the spigot portion  94 , the kettle valve part comprises two concentric annular shrouds: an inner shroud  98  and an outer shroud  100 . The diameter of the outer shroud  100  is such that it fits over the outer housing  52  of the heating chamber valve part and it has a beveled edge to aid location. 
     Between the spigot  94  and the inner shroud  98  is a sprung valve arrangement comprising a vertically movable valve member  102  which has at the top a valve head  104  which is biased towards a corresponding valve seat  106  by a compression coil spring  108 . The coil spring acts between the underside of the valve seat  106  and a ring  110  at the bottom of the valve member  102 . In the configuration shown in  FIG. 11 , an upward force is being applied to the lower ring  110  of the valve member thus lifting the valve head  104  away from the valve seat  106  to permit water to pass through the valve. Equally, however, it will be seen that when this force is removed, the coil spring  108  acts to close the valve and therefore prevent further passage of water. 
     The components provided on the heating chamber side of the valve arrangement comprise the outer housing  52  (mentioned previously with reference to  FIGS. 6 ,  7  and  8 ) having a central, chamfered opening which receives the inner shroud  98  of the kettle valve housing. This outer housing  52  therefore passes, during coupling of the two valve parts, between the inner and outer shrouds  98 ,  100  of the upper part. Inside the outer housing  52  is the annular sealing member  68  which provides a fluid-tight seal against the upwardly projecting annular wall  66  which is an integral part of the top of the heating chamber  58 . The sealing member  68  has a central annular protrusion which forms an upwardly open annular channel which receives and seals against the lower edge of the inner shroud  98  of the kettle valve part. 
     On the lower face of the sealing member  66  is an angled annular flange  112  which extends radially outwardly so that it has a degree of flexibility in the axial direction. 
     Beneath the sealing member  66  is a generally frusto-conical float valve member  114  which is able to move vertically but which is constrained in its downward travel by a valve stop member  116 . The top surface of the float valve member  114  presses against the angled annular flange  112  when it is in the upper portion of its travel. 
       FIG. 12  shows a perspective view from above of the dispensing chamber  44  with the upper cover removed.  FIG. 13  shows a vertical cross-section through part of the chamber with the upper cover in place. The main part of the dispensing chamber  44   a  is broadly bowl-shaped with the dispensing spout  45  in a distinct recess  44   c  at the center. Extending around part of the rear edge is a raised, generally horizontal platform portion  44   b  into which the outlet pipe  60  and vent pipe  62  from the heating chamber emerge. It will be noted that these two tubes  60 ,  62  extend vertically some way into the dispensing chamber. 
     Mounted outside the dispensing chamber (but shown in  FIG. 12  for reference) is an R48 steam switch  188  to which is attached the on/off rocker switch  54 . A vertical chimney  120  extends through, but is isolated from, the dispensing chamber  44  and opens just beneath the bimetallic actuator (not clearly visible in  FIGS. 12 and 13 ) of the steam switch  118 . This allows cool air to pass over the bimetallic actuator after it has operated in order to allow it to reset relatively quickly. 
     As may be seen most clearly from  FIG. 13 , the tube forming the outlet spout  45  extends vertically some way into the dispensing chamber  44  inside a concentric downwardly open tube  122  of slightly larger diameter which is mounted to the upper cover of the dispensing chamber. The downwardly open tube  122  extends down just short of the annular recess  44   c  in the center of the main part of the dispensing chamber  44   a.    
       FIG. 14  shows a schematic circuit diagram showing the main electrical connections between various parts of the appliance. To the left of the diagram may be seen the line, neutral and earth connections from the mains lead (not shown). The switch contacts of the steam switch  118  provided in the dispensing chamber are connected electrically in series between the line pole and the coil of a relay  124  (although not shown in this schematic diagram, some form of rectification might be provided). The contacts of the relay  126  are of the change-over type with the common contact  126   a  connected to the line pole. The normally-off relay contact  126   b  is connected to the heating element  76  provided on the base of the heating chamber  58 . Although not shown in the Figures, the electrical connection to this element  76  is made by means of a modified U-series control having its characteristic pair of overheat-protection bimetallic actuators which act on respective normally-closed contacts  128   a ,  128   b  on the line and neutral side respectively of the element. An indicator neon  130  is connected, in series with a suitable resistor  132 , across the element  76  to indicate when the element is energized. 
     The normally-closed relay contact  126   c  is connected to the central, line terminal of the cordless electrical connector  50 . The neutral and earth terminals are connected directly to the corresponding inputs from the mains lead. 
     To the right of the diagram in  FIG. 14  is depicted the conventional electrical arrangement found in a kettle. Thus, the heating element  134  is connected in series with the normally-open contact of the steam switch  48  and also in series with the normally-closed contacts  136   a ,  136   b  which are acted on by the overheat bimetals of a U17 control. Again, an indicator neon  138  and corresponding resistor  140  are connected across the element  134  to indicate when it is energized. 
     Operation of the embodiment described above with reference to  FIGS. 5 to 14  will now be described. 
     As with the previous embodiments, the appliance of this embodiment can be operated in two separate modes. In the first mode, the kettle  40  can be removed, filled and then replaced on the base. To start boiling, the on switch (not shown) is pressed to close the contacts of the steam switch  48 . In the normal state shown in  FIG. 14 , power can then be supplied through the cordless connector  50  to energize the element  134 . Unless the user switches off again, heating will continue until the water in the kettle boils which causes the steam switch  48  to operate and disconnect the power to the element. The kettle  40  can then be lifted up again and the boiling water poured out of its spout in a conventional manner. 
     However, if a user wishes to boil and dispense just a cupful of water, he or she can operate the appliance in a second mode of operation which will be described below. 
     When the appliance is first used, or the heating chamber  58  has otherwise been allowed to become empty, it must be filled with water. This is done by filling kettle  40  with water and replacing it on the stand  42 . This allows the water in the kettle  40  to drain through the valve arrangement shown in  FIG. 11  into the heating chamber. More particularly, as the kettle  40  is replaced on the stand, the lower end ring  110  of the valve member  102  in the kettle valve part is forced up against the force of the coil spring  108  by its contact with the inner annular projection of the sealing member  68 . This allows water to flow from the inside of the kettle  40 , through the valve spigot portion  94 , past the valve member  102  and into the heating chamber  58  through the center of the sealing member  68  and over the edges of the float valve member  114 . The vent tube  62  allows air to be displaced from the chamber even after the lower part  86  of the outlet tube has been covered. 
     As the level of water in the heating chamber  58  rises, the float valve member  114  will gradually be raised by the water until such time as it seals against the annular flange  112  on the lower face of the sealing member  68  with sufficient force to prevent any further water entering the heating chamber  58 . If the kettle  40  should now be lifted up again, the coil spring  108  will close the valve head  104  against the valve seat  106  inside the kettle valve housing, thus preventing leakage of water from the kettle. Similarly, the buoyancy pressure of the float valve member  114  against the compliant annular flange  112  at the bottom of the sealing member  68  will prevent water from spurting out of the lower part of the valve arrangement. When the kettle  40  is replaced, although the kettle side of the valve  104 ,  106  will be opened again, no further water will flow since the float valve member  114  will remain pressed against the annular flange  112 . 
     In order to operate the appliance in the second mode, the user must switch on the switch  54  provided at the top of the dispensing chamber. As will be appreciated by considering the circuit diagram of  FIG. 14 , this energizes the relay coil  124  to disconnect relay contacts  126   a  and  126   c  and connect contacts  126   a  and  126   b . This has two consequences. The first is that the kettle  40  cannot be operated since power is no longer being supplied to the cordless connector  50 , thereby ensuring that the two elements  76 ,  134  cannot be energized at the same time which would drain an excessive current for an ordinary domestic mains socket. The other consequence is that the element  76  on the underside of the heating chamber  58  is energized and begins to heat the water in the heating chamber. 
     During the initial stages of heating, the build-up of pressure inside the heating chamber  58  is limited by the vent tube  62  connected to the dispensing chamber  44  which is essentially at atmospheric pressure. This prevents water which has not been sufficiently heated from being ejected via the outlet tube  60  prematurely. It also reduces any tendency of the float valve member to  114  to ‘wobble’ against the sealing member  68 . Together with the compliant annular flange  122  this helps prevent further cold water entering the heating chamber during heating. 
     As the temperature of the water in the heating chamber  58  approaches boiling, the pressure builds up and begins to force water up the outlet tube  60  and so into the dispensing chamber  44 . As this continues, almost all of the boiling water in the heating chamber  58  is forced up the outlet tube  60  to fill the dispensing chamber  44 . Water will continue to be forced up the outlet tube until the water level in the chamber  58  falls below the lower end of the downward extension of the outlet tube  88 . 
     Turning to  FIGS. 12 and 13 , it will be seen that boiling water initially enters the side chamber  44   b  and thereafter drains into the main part of the chamber  44   a  towards the annular recess  44   c  in the center and so starts to fill the chamber main part  44   a . As water continues to enter the dispensing chamber  44 , the level between the downwardly open tube  122  and the upwardly extending outlet spout  45  rises until the water begins to flow over the top edge of the outlet tube  45  and so down through the spout into a user&#39;s cup. This sets up a siphon which causes virtually all of the water in the dispensing chamber  44  to be dispensed through the spout  45 . 
     Once all the water has been forced up from the heating chamber  58  via the outlet tube  60 , steam from the heating chamber  58  will be ejected from the top of the outlet tube  60  (as well as form the vent tube  62 ) and into the dispensing chamber  44 . This causes the steam switch  118  to switch off, thereby interrupting power to the relay coil  124  and so disconnecting the heating chamber element  76 . 
     When pressure in the heating chamber has subsided, the float valve member  114  drops down against its stop  16  which automatically refills the heating chamber  58  with water from the kettle  40 , assuming it is there and has sufficient water in it. If the kettle  40  is not there, the heating chamber  58  will be refilled next time it is replaced. The kettle  40  therefore acts as a convenient removable reservoir for the heating chamber. This allows a user to produce cups of boiling water repeatedly throughout the day without having to refill the kettle each time, without re-boiling the same water several times (which is often considered to harm its taste by removing dissolved oxygen) and, importantly, without wasting energy by boiling more water than is necessary. 
     If the heating chamber  58  is operated without any water in it, for example if there is no water in the kettle  40  to refill the chamber after a previous use, then one or other of the bimetals in the modified U-series control protecting the element  76  will operate to open the respective contacts  128   a ,  128   b.    
     Thus it will be seen that a highly versatile appliance is provided which can either be used as an ordinary kettle to heat a relatively large quantity of water or, if only a single cupful of water is required, it can be heated and dispensed very quickly and efficiently by means of the second mode of operation. The kettle  40  then acts as a removable reservoir in this mode of operation which is in itself convenient as it allows easy refilling. The provision of a relay to switch between the two elements avoids an electrical overload. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed herein as the best mode contemplated for carrying out this invention.