EP0209868A2 - Electric heater for a fluid container - Google Patents

Abstract

Electrical heating, which is particularly suitable for heating water, but also for edible fats or similar media, has a container (2) for storing the liquid to be heated and a water heater (21) integrated with the container (2). The liquid flows in a circuit from the container (2) into the continuous-flow heater (21), is deflected upwards in the latter, heated in an upward flow by tubular heating elements (17) lying outside the liquid, and thus into the container (2) under thermosiphon effect returned. Solids, such as lime, are separated from the liquid in the continuous-flow heater (21) and retained in a collecting space (18) located below the heating duct (7) and easily accessible for emptying.

Description

The invention relates to an electric heater for liquid containers, in particular for hot water devices, with at least one tubular heater.

For heating liquids in containers such as hot water storage, washing machines or the like. The radiator is generally assigned to the container in such a way that it heats the standing liquid therein until the desired temperature is reached. Despite possible flow reactions of the liquid as a result of the heating, this results in large temperature differences within the liquid in the container and an efficiency which is not always satisfactory. Especially when heating non-softened water, considerable drops also occur Quantities of solid matter in the form of lime, which deposits on the inside of the container and which both leads to a further deterioration in the efficiency and can also lead to cross-sectional constrictions which hinder the flow of the liquid. The cleaning of such containers for the purpose of removing the solids is usually very complicated and time-consuming.

The invention has for its object to provide a dielectric heating for liquid containers, which ensures an improved efficiency in a simple manner by continuous separation of solids.

To achieve this object, electrical heating of the type mentioned at the outset is characterized according to the invention by a flow heater which is connected to the container on the input and output sides and is heated by the tubular heating element and which has at least one lower collecting space for solids separation which can be emptied through a large opening. As a result, the liquid in the circuit through the container and the water heater and thus with constant thorough mixing is heated uniformly to the desired temperature, the resulting solids essentially not in the container, but in the collecting space of the water heater, from where it is much easier than can be removed from the liquid container. The flow of the liquid through the continuous-flow heater and thus through the container can, according to the invention, be achieved by thermosiphon action and / or by a mechanical pump, such as a circulating pump.

A particularly advantageous embodiment of the subject matter of the invention is that the continuous-flow heater has at least one flow heating channel which is heated by the tubular heating element from at least one side facing away from its side exposed to liquid, in particular from the outside. As a result, the tubular heating element or the tubular heating element does not come into direct contact with liquid, which in particular counteracts local overheating and ensures rapid heat transfer from the tubular heating element to the liquid, because the tubular heating element heats the wall of the heating duct over a large area and the liquid flows along this wall. As a result, the surfaces which come into contact with the liquid, in particular the liquid-carrying surfaces of the heating duct, can also be made very smooth and even, as a result of which the tendency to solid deposits is significantly reduced.

The thermosiphon effect of the instantaneous water heater can be achieved, for example, in a simple manner in that the input of the instantaneous water heater, for example directly from the container, in particular of the heating duct, is lower than the output, which also expediently opens directly into the container. The inlet and the outlet can lie vertically one above the other or the outlet can be provided laterally offset from the vertical to the inlet, in both cases it is expedient to provide flow paths within the flow heater that are as straight as possible between the inlet and the outlet. In the case of an inclined arrangement of the instantaneous water heater, which is designed, for example, in the manner of a heating cartridge, the angle of inclination can vary with the viscosity of the one to be heated Liquid can be adjusted so that this angle of inclination can be chosen flatter with lower viscosity.

A particularly compact and with respect to the Wirkun ^g s-grades even more improved embodiment of the heating results when the water heater at least partially integrated into the interior of container, in particular input and output side is set as a shaft to the container bottom. As a result, the instantaneous water heater forms a closed structural unit with the container and there are very short flow paths between the instantaneous water heater and the container. However, it is also conceivable to connect the instantaneous water heater to the container as a separate unit via pipe connections.

In a further embodiment of the invention, the flow heater has a downflow channel on the inlet side, via which the respectively cooler liquid can flow directly from the container into the flow heater. The case flow duct is preferably at least partially into the, ascending flow direction-heating channel, and / or about the same axis, so that the liquid on the We ^g from the container to the heating zone of the flow heater no further cooling is subjected to the heating channel and results in a very space-saving design of the water heater.

A very favorable flow behavior of the liquid can be achieved in that the upper end of the downflow channel, in particular above the container bottom, is provided higher than the outlet opening of the continuous-flow heater, in particular at the level of the container bottom, so that despite almost any container . form a favorable circulation flow is achieved within the container.

This is substantially improved by the fact that at least one flow guide element pointing away from the inlet flow of the downflow channel is provided for the outlet flow of the instantaneous water heater, which is preferably formed by the funnel-like widened end of the downflow channel that covers the outlet opening of the heating channel. If the downdraft duct and the heating duct are arranged in the same axis as the flow guide member or the outlet opening lying inside the container, the heated liquid coming from the flow heater is directed into the container away from the central axis of the flow guide member, while the liquid flowing to the flow heater is concentrated on an area immediately around this central axis.

On the design according to the invention, existing containers, for example burner-heated hot water boilers, can generally be converted well if the instantaneous water heater is designed for connection to the outside of the container and preferably for connection to an upright container wall lying on the input and output sides transversely to the heating duct Has connection openings. The instantaneous water heater can be connected to the container in an electrically isolated or galvanically isolated manner, so that problems due to electrolysis are hardly to be feared. In the case of connecting the instantaneous water heater to the outside of the container, this can be achieved, for example, by providing pieces of tubing made of non-conductive material, for example plastic, in the liquid-carrying connection connections as intermediate members are. The connection connections between the instantaneous water heater and the container can be designed in such a way that the instantaneous water heater is carried exclusively by these connection connections and therefore requires no further support or fastening.

To further increase the efficiency and to further improve maintenance, two or more separate, in particular identical and / or parallel, heating ducts emanate from the collecting space and preferably open into a mixing housing before the outlet of the instantaneous water heater, in particular at its opposite the entry of the heating ducts Side is provided with a closable access opening, so that a direct inspection and cleaning of the interior of the heating channels is easily possible.

A structurally simple design of the heating can be achieved in that the heating duct, which is ring-shaped in particular in cross section, and / or the downflow duct is each formed by at least one tube.

The use of tubes, in particular cylindrical tubes, also offers the possibility of attaching the tubular heater very easily in a heat-conducting connection. This can be done according to the invention in that the tubular heater is attached to the instantaneous heater or the heating duct as a, in particular, pre-stressed coil and is preferably combined with the associated wall in a heat-conducting manner by alloying or a similar solder-like connection.

It is conceivable to design the collecting space or the instantaneous water heater so that the collecting space through the upper, large-area opening of the instantaneous water heater, ie is accessible for emptying, for example, through the downdraft duct. However, emptying is much easier if the collecting space has a bottom cover and / or is formed by a pot or the like which can be removed from the water heater, so that the collecting space can be emptied from below in a simple manner. If a gate valve or the like is provided in each line connection of the instantaneous water heater to the container, the collecting space can be cleaned at any time after the line connection or line connections have been emptied, regardless of the container being emptied.

For the purpose of temperature control or dry-running protection, at least one receiving tube for the pull-out arrangement of the sensor of a temperature controller or the like is advantageously arranged adjacent to the tubular heater and / or in the liquid flow path in the continuous-flow heater. As a result, the temperature is monitored by means of the sensor, not in the container, but in or on the water heater, which further simplifies the maintenance and assembly of the electrical heating.

In order to achieve a particularly safe protection against dry-running, the receiving tube for the temperature sensor is expediently soldered adjacent to the tubular heating element on the latter and / or on the wall of the heating duct or fastened with clamps surrounding it in a heat-conducting manner.

The inventive construction is except for hot water boilers and boiler particularly well as a heater for washing machines, dishwashers ud ^g l .. Furthermore, with the inventive heating liquids other than water, for example, Frying fats are heated by fryers; In the case of deep fryers, too, the separate arrangement of a continuous-flow heater results in simple cleaning of the deep-fryer container and simple separation of the solids resulting from deep-frying.

• Fig. 1 eine erfindungsgemäße Beheizung im Axialschnitt,
• Fig. 2 eine Draufsicht auf die Beheizung gemäß Figur 1,
• Fig. 3 ein Schnitt nach der Linie III-III in Figur 1,
• Fig. 4 eine weitere Ausführungsform einer Beheizung in einer Darstellung entsprechend Figur 1,
• Fig. 5 eine Draufsicht auf die Beheizung gemäß Figur 4,
• Fig. 6 ein Ausschnitt der Figur 4 in vergrößerter Darstellung,
• Fig. 7 eine weitere Ausführungsform einer Beheizung in Ansicht auf die Anschlußseite,
• Fig. 8 die Beheizung gemäß Figur 7 in Seitenansicht,
• Fig. 9 ein Schnitt nach der Linie IX-IX in Figur 7,
• Fig. 10 ein Ausschnitt der Figur 8 in geschnittener und vergrößerter Darstellung,
• Fig. 11 der Ausschnitt gemäß Figur 10 in einer weiteren Ausführungsform,
• Fig. 12 ein weiteres Ausführungsbeispiel einer Beheizung in teilweise geschnittener Ansicht,
• Fig. 13 ein weiteres Ausführungsbeispiel einer Beheizung in einer Darstellung entsprechend Figur 7,
• Fig. 14 die Beheizung gemäß Figur 13 in Seitenansicht,
• Fig. 15 die Beheizung gemäß Figur 13 in Draufsicht.

The invention is explained in more detail below with further details using the exemplary embodiments illustrated in the drawings. They are shown in

• 1 shows a heating according to the invention in axial section,
• 2 shows a top view of the heating according to FIG. 1,
• 3 shows a section along the line III-III in FIG. 1,
• 4 shows a further embodiment of heating in a representation corresponding to FIG. 1,
• 5 shows a top view of the heating according to FIG. 4,
• 6 is a detail of Figure 4 in an enlarged view,
• 7 shows a further embodiment of a heater in a view of the connection side,
• 8 shows the heating according to FIG. 7 in a side view,
• 9 is a section along the line IX-IX in Figure 7,
• 10 shows a section of FIG. 8 in a sectional and enlarged representation,
• 11 the detail according to FIG. 10 in a further embodiment,
• 12 shows a further exemplary embodiment of a heating in a partially sectioned view,
• 13 shows a further exemplary embodiment of heating in a representation corresponding to FIG. 7,
• 14 the heating according to FIG. 13 in side view,
• 15 shows the heating according to FIG. 13 in a top view.

The heating 1 according to FIGS. 1-3 is assigned to a container 2, for example a hot water boiler, which is provided with inlet and outlet lines, not shown, for the liquid to be heated. The container 2 is formed essentially symmetrically to a vertical central axis 3, the heating 1 as a whole also lying in this central axis 3 with respect to its central axis. The heating 1 is arranged on the bottom 4 of the container 2 in the region of an opening 5 of this base 4 and partially projects through the central, for example circular opening 5 into the interior of the container 6.

The heating 1 has a vertical heating channel 7 with a circular cross section, which is delimited radially on the outside by a tubular wall 8 and radially on the inside by a tubular wall 9 which is axially aligned with the wall 8. The wall 9 encloses or delimits At the same time, a falling-flow duct 10, which lies in the heating duct 7 and is separated from it only by the wall 9, the lower end of which, approximately in the plane of the lower end of the wall 8, lies at the level of the circular liquid inlet 11 of the heating duct 7. The tubular wall 8 has at the upper end a flange 12 for sealed attachment to the underside of the container bottom 4, the width of the opening 5 being at least as large as the largest width of the heating channel 7. The upper end of the heating channel 7 lying at the level of this flange 12 forms its circular liquid outlet 13 opening directly into the container 6. The upper; The end of the wall 9 or the downdraft duct 10 is slightly funnel-like above the liquid outlet 13 to a width that is greater than the greatest width of the outlet 13 or of the heating duct 7 which has essentially constant cross sections over its height. As a result, the upper end of the wall 9 forms, in addition to a funnel-like inlet opening for the downflow channel 10, narrowing downward in a funnel-like manner down the width of the downflow channel 10, a flow guide member lying in a ring around the central axis 3 and pointing obliquely upward in axial section, which in plan view of the heating 1 completely covered the outlet 13 of the heating duct 7. Through the flow guide member 14, the liquid stream led into the heater 1 is thus effectively separated from the liquid stream led out of the heater 1 into the container 2, such that the heated liquid leaving the heater 1 uniformly around the central axis 3 along the wall of the Container 2 guided upwards, deflected downward in the upper region of the container 2 and finally fed back to the downflow channel 10 in the circuit for further heating.

The outer wall 8 of the heating duct 7 is provided on its outer side 16 facing away from the liquid-loaded inner side 15, namely on the outer circumference, with an electric tubular heating element 17 which is close-fitting and thus in a good heat-conducting connection on this side 16, for example by solder-like Apply, is attached. The tubular heater surrounds the wall 8 in a helical manner, it being possible for two or more helical, separately electrically connectable radiator filaments to be arranged in the manner of a multi-start filament in order to be able to operate the heater 1 with different outputs. The tubular heater 17 extends essentially over the entire length of the heating duct 7 or the wall 8.

Below the entrance 11 of the heating duct 7 there is a deflection and collecting space 18, the central axis of which coincides with the central axis 3 and the width of which is at least as large as the largest width of the heating duct 7, such that the heating duct 7 extends downward over its entire cross section to the collection room 18 is open. The collecting space 18 is formed by a pot 19, which is attached to a lower flange 20 of the wall 8 in an easily detachable but sealed manner. The liquid emerging from the lower outlet opening of the downflow duct 10 lying in the plane of the inlet 11 is deflected radially outward and upward into the heating duct 7 in the collecting space 18, solids sinking into the relatively low-flow lower region of the collecting space 18 and settling on the floor deposit the collection room 18. Any solids which are deposited on the walls of the heating duct 7 and which at least partially continuously become detached due to the thermal stresses that occur tend to be in view of the relatively low flow velocity in the heating duct 7. also to sink to the bottom of the collecting space 18. After the pot 19 has been removed, it can be emptied and, in addition, the heating duct 7 is then completely accessible from below over its entire height, so that its walls can be easily cleaned.

Due to the design described, the heater 1 has a water heater 21 integrated with the container 2, which heats the container contents in the circuit. The actual heating zone lies in the area of the heating duct 7, in which the flow acc. Arrow 22 is directed from the bottom up.

In FIGS. 4 to 15, parts corresponding to one another have the same reference numerals as in FIGS. 1 to 3, but in FIGS. 4 to 6 with the index "a", in FIGS. 7 to 10 with the index "b" in FIG 11 with the index "c", in FIG. 12 with the index "d" and in FIGS. 13 to 15 with the index "e".

In the embodiment according to FIGS. 4 to 6, the container base 4a is provided with a base flange 5a, to which the tubular wall 8a delimiting the heating channel 7a on the outer circumference is fastened with its upper flange 12a. The two flanges lying against one another are secured with a releasable profile ring 23 with the interposition of an annular seal 24 surrounding them.

The wall 8a extends over the entire height of the continuous-flow heater 21a, in such a way that it also delimits the collecting space 18a at the same time and projects downwards relative to the lower end of the wall 9a by the height of the collecting space 18a. At the lower end of the wall 8a, a removable bottom cover 25 is attached so that the inside the wall 8a is accessible over its entire width after removing the bottom cover 25. The upper end of the wall 9a forms a plurality of fastening tabs 26, which are evenly distributed around the central axis 3a and protrude approximately radially outward and which are fastened to the inside of the container bottom 4a with bent ends. After removing the wall 8a, the outside of the wall 9a is thus very easily accessible.

As shown in FIG. 6 in particular, the tubular heater 17a for the system on the associated side 16a of the wall 8a can also be flattened, for example triangular in cross section, so that there is an even better heat transfer from the tubular heater 17a to the wall 8a. Adjacent to the tubular heating element 17a, at least one receiving tube 27 is fastened on the same side 16a of the wall 8a in a highly heat-conducting manner, which is used for receiving the temperature sensor 28 of a temperature regulator filled, for example, with an expansion fluid. In the same or a similar manner, a receiving tube for the temperature sensor of dry-running protection can also be provided, this receiving tube expediently being in direct heat-conducting contact with the tubular heating element.

FIGS. 7 to 10 show a continuous-flow heater 21b which has connection openings 29, 30 located transversely or at right angles to the direction of flow arrow 22b of a plurality of heating channels 7b for connection to the container (not shown in more detail). The pot 19b delimiting the collecting space 18b has its pot opening on the underside, which is closed with a removable cover 25b. At the top of the pot 19b, three mutually parallel, in a common axial plane standing pipe pieces 8b are connected each limit a heating channel 7b and are provided on the outer circumference with a separate helical tubular heater 17b. The clear distance between adjacent pipe sections 8b is smaller than their diameter. The upper ends of the pipe pieces 8b and thus the heating channels 7b are connected to the bottom of a likewise pot-shaped, common mixing housing 31, the upper pot opening of which is also closed with an easily detachable cover 32. The inlet connection opening 29 of the instantaneous water heater 22b is provided in a wall of the pot 19b, while the outlet connection opening 30, which is parallel to the axis and vertically above it, is provided on the associated wall of the mixing housing 31. The two connection openings 29, 30 can be formed by projecting connection pieces 33, 34. As a result of this design, the instantaneous heater 21b can be subsequently connected to the outside of a container in a simple manner. Furthermore, the heating channels 7b are easily accessible after removing the covers 25b, 32 for the purpose of cleaning or the like.

On the outer sides of the tube pieces 8b, a common receiving tube 27b is attached for a temperature sensor serving to protect against dry-running. The receiving tube 27b, which is tangential to all the pipe sections 8b, lies in the region of each heating duct 7b between two turns of the associated tubular heating element 17b, which it can touch directly. The temperature sensor is inserted into the receiving tube 27b, which is open at one end, so that it can be pulled out at any time and, for example, replaced. The same applies in the case of a second receiving tube 35, which is in the flow path of the liquid within the flow heater 21b, namely in the upper region of the collecting space 18b. The closed end of the receiving tube 35 lies within the collecting space 18b, while the other open end of the receiving tube 35, which penetrates a wall of the instantaneous water heater 21b to the outside in a sealed manner, is freely accessible on the outside of the instantaneous heater 21b. As a result, the associated temperature sensor, which is expediently assigned to a temperature controller, can be replaced at any time; for this purpose, the receiving tubes are also essentially straight or only slightly curved at most so that the temperature sensor can be inserted or pulled out with sufficient ease.

Even in the case of a continuous-flow heater according to FIGS. 7 to 9, the tubular heating elements 17c according to FIG. 11 can have flattened contact surfaces or be triangular in cross section.

The instantaneous heater 21d according to FIG. 12 is also designed for the arrangement on the outside of a container. The heating duct 7d, which is circular in cross section, is delimited by two coaxial, tubular walls 8d, 9d, the outer wall 8d being provided on the outside with at least one tubular heating element 17d and the inner wall 9d on the inside with at least one tubular heating element 17d, so that results in a substantially enlarged contact area for heating the liquid flowing through the heating channel 7d. Such a configuration would also be conceivable in the case of the arrangement of a downdraft duct according to FIGS. 1 to 6, the wall of the downdraft duct then lying within the inner tubular heating element 17d. To increase the efficiency or to avoid heat losses, the outer tubular heater 17d or the associated wall 8d is included a heat insulation 36 and the inner tubular heater 17d covered with a heat insulation 37. The inner insulation 37 can completely fill the inner cavity of the wall 9d. The inlet connection opening 29d of the continuous-flow heater 21d or the associated connection piece 33d is expediently provided on the pot 19d delimiting the collecting space 18d, which can for example be detachably screwed onto an external thread of the outer tubular wall 8d. If the inner wall 9d is also fastened to this pot 19d, it can be completely pulled out of the outer wall 8d by loosening the pot 19d, as a result of which the entire instantaneous water heater 21d can be cleaned very easily.

As shown in FIGS. 13 to 15, the inner wall 9e of the annular heating duct 7e which in this case deviates from the circular shape in cross section can also be arranged in a hanging manner in the outer wall 8e. The upper end of the wall 9e is attached to a switch box 38 for the tubular heater 17e, which at the same time forms the upper, releasable end cover of the outer wall 8e; as a result, the inner wall 9e including the tubular heating element 17e can be pulled out of the outer wall 8e with the switch box 38 upwards. In the illustrated embodiment, tubular heating elements 17e are only provided on the inside of the inner wall 9e.

The pot 19a delimiting the collecting space, which is shown in the removed state in FIG. 14, is detachably attached to the underside of the outer wall 8e, so that it can be emptied at any time. If the pot 19e and the switch box 38 are removed, the entire interior enclosed by the wall 8e is freely accessible for maintenance.

As FIG. 14 further shows, the container 2e indicated by dash-dotted lines is provided on an upright or vertical container wall 39 with two mutually parallel, essentially vertically superimposed connecting pieces, the spacing of which is adapted to the distance between the connecting pieces 33e, 34e. The connecting pieces of the instantaneous water heater 21e are connected to the connecting pieces of the container 2e by means of attached connecting sleeves 40 made of rubber or the like. These connecting sleeves 40 are secured, for example, with clamps. As a result, the water heater 21e can be completely removed from the container 2e at any time.

A continuous-flow heater is also conceivable, the outer wall of which has a bulbous, flattened or oval shape corresponding to the wall 8e according to FIG. 15, on the outside of which at least one tubular heating element is wound, similar to the embodiment according to FIGS. 7 to 9. The wall can be closed at the bottom and / or top with a removable cover corresponding to its cross-section, which has a connection piece for the supply or discharge of the liquid to be heated. Furthermore, the wall can consist of sections assembled in its longitudinal direction, each of which carries at least one separate tubular heating element, so that the heating power of the instantaneous water heater can be increased or decreased by adding or removing such sections, which can be of identical design. The sections expediently engage with one another with their end faces in a form-fitting and sealed manner, these end faces being able to be designed in such a way that they are equally suitable for the form-fitting, sealed engagement the end covers are suitable. The flattened design of the instantaneous water heater results in favorable dimensions for space-saving accommodation. The outer wall of the instantaneous water heater can also have a barrel shape, for example be bulged toward the center of its length, such that its cross sections are smaller in the area of its ends than in the area of the center of its length.

Claims (10)

1. Electrical heating for liquid containers, in particular for hot water devices, with at least one tubular heater, characterized by an on the input and output sides of the container (2) connected by the tubular heater (17) heated flow heater (21), the at least one has lower collecting space (18) which can be emptied through a large opening for solids separation. 2. Heating according to claim 1, characterized in that the continuous-flow heater (21) has at least one flow heating duct (7), the wall (8) of at least one side (16) facing away from its liquid-charged side (15), in particular from it Outside, through the tubular heater (17) is heated. 3. Heating according to claim 1 or 2, characterized in that the input (11) of the water heater (21), in particular the heating channel (7), is lower than the output (13). 4. heating as claimed in any one of the preceding claims characterized in that the heater (21) at least partially integrated into the container interior (6), in particular input and output side than at the loading bay Senior Citizen _{h e} r-base (4) is scheduled. 5. Heating according to one of the preceding claims, characterized in that the flow heater (21) on the input side has a downflow channel (10), which preferably at least partially in the ascending flow direction (arrow 22) having the heating channel (7) and / or approximately coaxially with Heating duct (7) is located, the upper end of the downflow duct (10), in particular above the container bottom (4), being higher than the outlet opening (13) of the continuous-flow heater (21), in particular at the container bottom (4) ) is provided and advantageously a flow guide member (14) pointing away from the inlet flow of the downflow channel (10) is provided for the outlet flow of the instantaneous water heater (21), which preferably extends through the funnel-like extension that covers the outlet opening (13) of the heating channel (7) End of the downflow channel (10) is formed. 6. Heating according to one of the preceding claims, characterized in that the flow heater (21e) is designed for connection to the outside of the container (2e) and preferably for connection to an upright container wall (39) lying transversely to the heating duct (7e) and has outlet openings (29e, 30e) on the output side. 7. Heating according to one of the preceding claims, characterized in that from the collecting space (18b) two or more separate, in particular identical and / or parallel heating channels (7b), which preferably before the output of the instantaneous water heater (21b) in a mixing housing ( 31), which is provided in particular on its side opposite the inlet of the heating channels (7b) with a closable access opening. 8. Heating according to one of the preceding claims, characterized in that the heating channel (7) and / or the downflow channel (10), in particular with an annular cross section, is in each case formed by at least one tube and / or that the tubular heating element (17) is, in particular biased coil attached to the flow heater (21) or on the wall (8) of the heating channel (7) and preferably by alloying or the like. is thermally combined with the associated wall. 9. Heating according to one of the preceding claims, characterized in that the collecting space (18a or 18) has a bottom cover (25) for emptying and / or by a pot (19) or the like which can be removed from the water heater (21). is formed. 10. Heating according to one of the preceding claims, characterized in that adjacent to the tubular heater (17b) and / or in the liquid flow path in the water heater (21b) at least one receiving tube (27b, 35) for the pull-out arrangement of the sensor of a temperature controller or the like . is arranged, preferably for, in particular Other temperature sensors arranged for dry-running protection are soldered adjacent to the tubular heating element and / or are soldered to the wall of the heating duct or are fastened with clips enclosing the heat-conducting tube.

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