GB1591230A

GB1591230A - Control means for a heating system and a heating system controlled thereby

Info

Publication number: GB1591230A
Application number: GB48747/77A
Authority: GB
Original assignee: Tour and Andersson AB
Current assignee: Tour and Andersson AB
Priority date: 1977-01-28
Filing date: 1977-11-23
Publication date: 1981-06-17
Also published as: FI61091C; SE7700891L; FI780075A; DE2803596C2; FR2379034A1; SE403826B; FR2379034B1; DE2803596A1; FI61091B

Description

(54) CONTROL MEANS FOR A HEATING SYSTEM AND A HEATING SYSTEM CONTROLLED THEREBY (71) We, TOUR & ANDERSON AKTIEBOLAGET, A Company limited, organized under the laws of the Kingdom of Sweden, of Svardlangsvagen 46, Johanneshov, Stockholm, Sweden, do hereby declare the invention, for which we pray that a patent may be gratned to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to heating systems and is particularly concerned with control means including a thermostatically controlled by-pass valve for the systems.

It is well known that optimum economy of heat is obtained when a heating system is driven at a high water temperature, but it is also well known that a high temperature in a heating system with radiators will impair user comfort and, with a very high surface temperature of the radiators, may be unhealthy. Therefore, it has become customary to provide the heating systems with a so-called by-pass conduit, whose purpose is to receive part of the return heat transfer medium, below for simplicity called the "return water", and to feed this into the feeder conduit, which is otherwise, in the usual way, fed with hot water from, for example, the heating boiler. In this way a mixture of hot water and cooler return water has been provided in the feeder conduit, and the boiler may be driven at a higher water temperature while the feeder conduit will contain water of a more moderate temperature.

In such systems of this kind, a three-way valve has been arranged in the connection of the by-pass conduit to the feeder conduit, the valve being thermostatically controlled in order to maintain a constant temperature of the output water therefrom to the feeder conduit. The value of this constant temperature of the output water to the feeder conduit has, as a rule, also been manually controllable. The three-way valve may, of course, be provided either between the feeder conduit and the by-pass conduit or between the return conduit and the by-pass conduit.However, as the thermostatically controlled three-way valve is preferably controlled by the temperature of the water in the feeder conduit, it has been found natural to provide the thermostat in the interior of the three-way valve, so that it is washed by the output water from the valve to the feeder conduit, and in this case it has therefore also been found most convenient to provide the three-way valve between the feeder conduit and the by-pass conduit.

There is, however, also another type of heating system using a thermostatically controlled by-pass conduit in which the threeway valve should, instead, be provided between the return conduit and the by-pass conduit. In this system it is assumed that some of the radiators therein are individually thermostatically controlled according to the respective temperatures of the rooms heated thereby, while other radiators do not have such individual thermostatic control. It has been found that if such an individual thermostat influences in a given direction a valve associated with one or more radiators, this will influence the temperature of the water in the return conduit.Perhaps this may most simply be explained in the following way: Assuming that the temperature in the heated room shows a tendency to decrease to a value below the deisred level, the individual radiator thermostat will indicate a need for an increased feed of warm water from the feeder conduit to the radiator, and the total stream through this individual control valve will be correspondingly increased.

This means that a greater amount of warm water will pass through the radiator, but any portion of this warm water will remain in the interior of the radiator for a shorter while so that it will not cool to the same extent as previously. In other words, this means that the return water temperature will rise when an indication is given for more heat to be given off from the radiator or radiators associated with the radiator valve. This increase of the return water temperature may be used as a control signal for a corresponding change in the temperature in the feeder conduit so that the temperature of the feeder conduit water is increased in order to give off an increased amount of heat from all the radiators in the system.

Thus, it should be observed that this increased feed of heat not only takes place to the individually thermostatically controlled radiators, but also to the nonthermostatically controlled radiators, but also to the non-thermostatically controlled radiators in the system, so that one will in this way get firstly a partial re-adjustment according to l:he initially indicated need for an increased feed of heat given by one or more of the individually thermostatically controlled radiators, and secondly a corresponding increase of the feed of heat to all the remaining radiators in the system.

The present invention applies principally independently of whether the three-way valve (hereinafter referred to as the "bypass valve") is provided in the feeder conduit or in the return conduit.

Now, it has been observed that the amount of heat given off from a radiator in either of the systems mentioned above, should not only be dependent upon the actual room temperature but, in order to increase user comfort, also some circumstances in the outer atmosphere should be allowed to influence the temperature of the radiators. Thus, at a low temperature of the air outside a building, a somewhat stronger radiator heating may be desirable than at high temperature, and a strong wind or increased moisture content of the air may cause an increased cooling of the outer walls of the building, which will also create a greater need for heat inside.On the other hand, sunshine on to an outer wall surface may cause heating by radiation, which adds to the convection or internal radiation heating derived from the radiators, and thereby, in order to increase user comfort, the convection and radiation heating of the radiators may be correspondingly decreased by a change of the temperature on their surface through a change of the temperature of the water in the feeder conduit.

Hitherto, one could only overcome the intricate problems emanating from this by use of very complicated arrangements (socalled "climatization systems"). Such arrangements were usually electronically controlled, and to the output control circuit thereof was connected a motor which in turn compulsorily influenced the adjustment of the thermostatically controlled by-pass valve to change the temperature in the feeder conduit.

According to the present invention there is provided control means for a heating system including a feeder conduit, a return conduit and a by-pass conduit for heat transfer medium, such as water, the control means comprising: a thermostatically controlled by-pass valve having a valve housing with three ports for connection of the valve to the by-pass conduit and in one of the feeder and return conduits and a thermostat mechanically engaged with a valve body within the valve housing so that it can be influenced by the temperature of heat transfer medium in the valve to adjust the position of the valve body relative thereto and thereby vary the amount of medium passing through the by-pass conduit and/or said one of the feeder and return conduits; an electro-thermal motor mechanically engaged with the thermostat and capable of adjusting the position of the thermostat and the valve body relative to the valve housing in accordance with the temperature of the motor; and electro-resistive means capable of sensing a change in a condition (e.g.

temperature) of the environment around the sensing means and electrically connected to the motor to adjust the temperature thereof upon sensing said change.

Further according to the present invention there is provided a heating system including control means as described in the immediately preceding paragraph.

In the control means of the present invention, the usual adjustment of the by-pass valve according to the temperature of the heating medium is created by the thermostat influencing the valve body, and the influence from the aforementioned environmental condition or conditions is created by providing a mechanical bias in the valve housing to the mechanical force created by the thermostat. In order to ensure that the two forces can be added together without substantial disturbance, and in order that they should thereafter follow at least approximately the' same characteristic, it is an advantage that both forces are created by converting a deviation of condition (e.g.

temperature) into a movement of the valve body in the valve housing and it is important that there be no disturbances created by temperature changes in the connection between the sensing means and the electrothermal motor. In practice, it has been found that the latter object can only be met if the connection is an electrical connection since this forms the most stable signal transfer means available.

The climatization systems mentioned above in connection with prior proposals compulsorily influence the by-pass valve primarily according to the temperature of the outside atmosphere, and although the electro-resistive means of the control means of the present invention need to be limited to sensing temperature change, the invention will nevertheless hereinafter be described with reference to such change in the environment around the sensing means.

It will be appreciated that changes in one or more conditions of the said environment may be sensed by the sensing means.

Where the electro-resistive means is intended to sense temperature changes, it will conveniently comprise a thermistor, preferably with a power source between the thermistor and the motor.

Conveniently the electro-thermal motor comprises a heating element capable of transferring heat to means whose overall length varies on heating (i.e. by contraction or expansion) to adjust the position of the thermostat and the valve body. Said adjustment means (whose length varies) may engage with the thermostat through rod means axially aligned with the valve body.

The adjustment means preferably comprises a bi-metallic spring member, for example a helical spring, which provides expansion and contraction. The adjustment means may be engaged with a first seat carried by a casing of the electro-thermal motor and with the thermostat, and, where the force capable of being applied to the thermostat by the motor is manually adjustable, the motor casing conveniently comprises a cover supporting the first seat, the cover being axially advanceable relative to the remainder of the casing to adjust the position of the first seat and thereby manually adjust said force. The motor may comprise a tubular coil carrier on which the heating element is wound and which extends around said adjustment means; the heating element is conveniently supplied with power from the aforementioned power source.

Embodiments of control means in accordance with the present invention will now be described in combination with two different heating systems, with reference to the accompanying drawings, in which: FIGURE 1 is a schematic representation of a heating system including the by-pass valve of the control means in a feeder conduit; FIGURE 2 is a schematic representation of a heating system including the by-pass valve of the control means in a return conduit, and FIGURE 3 is a sectional elevation of the control means which may be used with suitable adjustments in either of the heating systems represented in FIGURES 1 and 2.

In the heating system represented in FIGURE 1, there is provided a heater vessel 10, such as a boiler, from which a hot water conduit 11 runs to a thermostatically controlled three-way by-pass valve 12. From the by-pass valve 12 a feeder conduit 13', 13" extends to a system of heat radiators, in common indicated by means of the block 15 with a pump 14 in the feeder conduit to ensure the circulation and feeding of warm water to the radiators. Of course, the pump 14 may instead be provided in a return conduit 16. From the radiators the return conduit 16 runs to a junction 17, from which extends firstly a conduit 18 to the vessel 10, and secondly a by-pass conduit 19 to the by-pass valve 12.

The system hitherto described and known per se, functions in the following way: Hot water is fed from the vessel 10 through the conduit 11 to the by-pass valve 12, where it is mixed with cooler water passing through the by-pass conduit 19 from the return conduit 16, so that a suitable temperature is obtained of the water entering the feeder conduit 13', Inside the bypass valve 12 is provided a thermostat which senses the temperature of the warm water given off to the feeder conduit 13', and if the thermostat determines that the temperature of the water in the feeder conduit 13' deviates from the desired value, it will control either the feed of cooler water from the return conduit 16 and the by-pass conduit 19, or the feed of hot water from the vessel 10 to the main conduit 11, or finally both of these matters, by influencing the valve openings concerned, so that the desired temperature in the feeder conduit 13' is restored.

Sometimes, the desired temperature has been manually adjustable in systems of this type which are known, said adjustment taking place by means of a separate adjustment means, which was located where, in the system according to the invention, an electrothermal motor 20 is situated; accordingly, a bias adjustment of the thermostat in the by-pass valve 12 could take place manually.

In the present invention, of course, such a bias adjustment may still be possible, but it is essential that a bias adjustment can take place according to the conditions of the outside atmosphere, especially its temperature.

For this purpose, a sensor 21 is provided out-of-doors and is electrically connected to the electro-thermal motor 20 of the by-pass valve 12. This arrangement functions so that when an increase in temperature outdoors is indicated by the sensor 21, an adjustment of the motor 20 is created electrothermally and acts upon the thermostat in the by-pass valve 12-whereby an increased flow of cooler water from the return conduit 16 and the by-pass conduit 19 and/or less hot water from the vessel 10 and the main feeder conduit 11 is fed to the feeder conduit 13', and the temperature of the water in the feeder conduit 13' decreases proportionally, or vice versa.

In the heating system represented in FIGURE 2, similar parts to those found in FIGURE 1 have been indicated by the same reference numerals. In this case, however, a by-pass valve 22 has been provided in the return conduit 16, 18 so that the thermostat therein will react according to the temperature of the water in the return conduit in order to adjust the proportion of cooler water from the return conduit 16 to hot water from the main feeder conduit 11 and the vessel 10. The cooler water derived from the return conduit is, in this arrangement, known per se, fed from the by-pass valve 22 to a junction 23 by means of a by-pass conduit 24.In the by-pass valve 22, the thermostat is provided with such an action that it will, with an increase in temperature of the return water in the conduit 16 (which will, in the manner mentioned above, indicate an increased need for heat in the heated space) decrease the feed of cooler return water through the by-pass conduit 24 to the junction 23 and/or increase the feed of water from the return conduit 16 through the conduit 18 to the vessel 10 and thereby also automatically increase the feed of hot water from the vessel 10 through the main feeder conduit 11 to the junction 23. In this way, the temperature of the water in the feeder conduit 13' is increased, and the existing need for an increased feed of heat to the space controlled with respect to its temperature is satisfied.It should be observed that in this case the signal for adjustment of the by-pass valve 22 was given by one or more individual thermostats connected to heat radiators in the block 15, indicating an increased need for heat in the space or spaces respectively heated by the radiators concerned, whereby the radiator valves were opened to let through a greater quantity of warm water so that the temperature in the return conduit also increased.

Also in this case, however, the thermostat in the by-pass valve 22 gets a mechancial bias tension through the electrothermal motor 20, which is electrically connected to the outdoor sensor 21, when the outdoor temperature increases. If the temperature of the outside atmosphere should increase, this will mean a decreased cooling of the outer walls of the temperature controlled space, and the feeder conduit temperature should therefore be a little less in order that the external increase in temperature shall be compensated for in advance. This takes place by creating a mechanical bias force on the by-pass valve thermostat of such a direction that the amount of cooler return water passing through the by-pass conduit 24 is increased simultaneously as the amount of hot water through the main feeder conduit 11 from the vessel 10 is decreased.

Now, it has been found that there may be certain difficulties in causing the by-pass valve 12 or 22 to function Immaculately.

The by-pass valve is thermostatically controlled, in the one case (12) by the temperature of the water in the feeder conduit 13', and in the other case (22) by the temperature of the return water in the return conduit 16, and this thermostatic control has a given inertia, determined by the time constant of the reaction of the thermostat for a changed state of temperature. If one would now try, by quick acting means, e.g. a purely mechanical power transfer from the outdoor sensor 21, to influence the thermostat in the by-pass valve 12 or 22 respectively, then this influence would necessarily take place over a small time constant, and the essential difference in time constants between the thermostat bias on the one hand, and the sensor bias on the other hand, would result in over-control so that self-oscillations would build up in the valve and the valve would clatter and be unstable.

This lack of stability is alleviated by the present invention with the thermostat being thermally influenced on the one hand by the temperature in the feeder conduit 13 ' or the return conduit 16, and on the other hand by the electro-thermal motor 20 which is in turn influenced by the conditions of the outdoor atmosphere, together with the fact that both influences take place totally within the by-pass valve in the presence of substantially equally great quantities of thermally active masses, whereby both influences take place by exactly or approximately the same time constants. No upset of the time constant derived from the outdoor atmosphere conditions will exist due to the transfer from the sensor 21 because this transfer takes place in a way free from inertia, i.e. practically without delay of time.The time constant of the sensor adjustment therefore will be completely determined by the conditions in the interior of the by-pass valve 12 or 22, and consequently it will be practically equal to the time constant of the thermostat bias, i.e. the direct adjustment of the thermostat under the control of the temperature in the feeder conduit 13 or the return conduit 16.

FIGURE 3 shows an advantageous form of execution of the by-pass valve 12 or 22.

The by-pass valve shown in FIGURE 3 has three ports 26, 27 and 28 in a housing 36. When the valve is connected into a system according to FIGURE 1, the port 26 forms the outlet to the feeder conduit 13', the port 27 is connected to the conduit 11 from the vessel 10, and the port 28 receives cooler water from the by-pass conduit 19.

When the valve is included in a system according to FIGURE 2, the port 26 is connected to the return conduit 16 for the cooler return water, the port 28 is connected to the continuation 18 of the return conduit 16 to th vessel 10 and the port 27 is, in this case, connected to the by-pass conduit 24.

A valve body is provided in the valve and comprises parts 30, 32 and 33. The valve body is under the influence of a thermostat 31, with the shaft part 32 being connected to or contacting between the thermostat and the valve body part 30. The thermostat-31 is also engaged by the axial arm-cross part 33, between whose arms water may pass essentially freely. The arm-cross part 33 is engaged by and under bias compression from a spring 34 housed within a cylindrical spring casing 35, the bias compression having such a direction that the spring 34 tends to increase the opening between the part 30 and a cooperating valve seat 29. The action of the thermostat 31 is such that, when heated, it displaced the shaft part 32 in a direction against the action of the spring 34, and therefore tends to decrease the valve opening 29-30.The thermostat is washed by the feeder conduit water in the arrangement according to FIGURE 1 and by the return conduit water in the arrangement according to FIGURE 2, and the magnitude of the valve opening 29-30 therefore will principally be determined by the said temperature.

In the parts hitherto described the by-pass valve is known per se. However, it should be observed that the thermostat 31 is, in the arrangement according to the present invention, freely hovering in the sense that it is not rigidly connected to any part of the valve housing 36 but engages at one end with the end of the shaft part 32 and at its other end with one end of a rod 37 associated with an electro-thermal motor 38. The electro-thermal motor may be made in many different ways, and the specific embodiment shown in FIGURE 3 is therefore only to be regarded as an example.

In this embodiment, the electro-thermal motor 38 comprises a cylindrical casing 39 with a flat cover 40 screwed thereto from which pressure means in the form of a bolt 41 extends inwardly into the casing. At its remote end the bolt 41 carries a disc 42, which forms a first seat for bi-metallic means whose dimensions will vary according to its temperature. Preferably, the bimetallic means is in the form of a helical spring 43 of a bifilaric material whose other end engages a spring seat 44 provided at the other end of the rod 37. The bi-metallic means 43 consequently will be subjected to a change of shape dependent upon its temperature and in order to vary the temperature, it is surrounded by a heat winding, comprising a resistance wire coil 45 on a winding support 46. The resistance wire coil 45 in turn is electrically connected at 47 to a current source 48 and a thermistor 49.

When the thermistor 49 is influenced by a change of temperature, the strength of the current created by the source of current 48 will also be changed. This current passes through the heater coil 45 with a consequent change of temperature and this change of temperature reacts in turn on the temperature of the bi-metallic means 43 which will either extend or contract in its axial direction. As the bi-metallic means 43 is rigidly supported at its one end against the bolt 41 and the disc 42, its other end, that is the end which engages the spring seat 44, will be displaced and this displacement will be transferred by the rod 37 to the thermostat 31.

It will now be understood that both the reaction movement proper of the thermostat and the reaction movement of the bimetallic means 43 will cause a displacement of the valve body with the consequence that the function mentioned above in connection with FIGURES 1 and 2 is provided.

A possibility for manual displacement in order to pre-set the valve exists by the cover 40 being connected to the cylindrical casing 39 by a threaded connection 50. If the cover 40 is turned in one or the other direction the cover, along with the bolt 41, will be displaced to a corresponding degree and will in turn cause an increase or decrease of the load on the bi-metallic means 43.

When, in the above, the features of the present invention were described, details which are inessential to these principles (such as packings between the electrothermal motor 38 and the valve housing 36 and the fixture of the electro-thermal motor 38 to the valve housing 36) have been omitted for clarity.

In FIGURE 3, arrows indicate the direction of movement of the water when the by-pass valve is used in a system according to FIGURE 2. The man skilled in the art will understand, from the above description, the movement of water when the valve is instead used in a system according to FIG URE 1. Double arrows in FIGURE 3 indicate movement of water from the return conduit 16, before this water has yet been distributed between the ports 27 and 28, whereas single arrows indicate the movement from the return conduit to each of the two ports 27 and 28. The movement from the port 26 to the port 27 is controlled by means of the valve opening between the valve body part 30 and its valve seat 29, whereas the movement from the port 26 to the port 28 is determined by means of a valve opening between a valve seat 51 on an intermediater wall 53 of the valve housing and a co-operating surface 52 on the valve body part 33. It will immediately be seen that the valve openings are closed and opened in counter time.

WHAT WE CLAIM IS: 1. Control means for a heating system including a feeder conduit, a return conduit and a by-pass conduit for heat transfer medium, such as water, the control means comprising: a thermostatically controlled by-pass valve having a valve housing with three ports for connection of the valve to the by-pass conduit and in one of the feeder and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. also engaged by the axial arm-cross part 33, between whose arms water may pass essentially freely. The arm-cross part 33 is engaged by and under bias compression from a spring 34 housed within a cylindrical spring casing 35, the bias compression having such a direction that the spring 34 tends to increase the opening between the part 30 and a cooperating valve seat 29. The action of the thermostat 31 is such that, when heated, it displaced the shaft part 32 in a direction against the action of the spring 34, and therefore tends to decrease the valve opening 29-30.The thermostat is washed by the feeder conduit water in the arrangement according to FIGURE 1 and by the return conduit water in the arrangement according to FIGURE 2, and the magnitude of the valve opening 29-30 therefore will principally be determined by the said temperature. In the parts hitherto described the by-pass valve is known per se. However, it should be observed that the thermostat 31 is, in the arrangement according to the present invention, freely hovering in the sense that it is not rigidly connected to any part of the valve housing 36 but engages at one end with the end of the shaft part 32 and at its other end with one end of a rod 37 associated with an electro-thermal motor 38. The electro-thermal motor may be made in many different ways, and the specific embodiment shown in FIGURE 3 is therefore only to be regarded as an example. In this embodiment, the electro-thermal motor 38 comprises a cylindrical casing 39 with a flat cover 40 screwed thereto from which pressure means in the form of a bolt 41 extends inwardly into the casing. At its remote end the bolt 41 carries a disc 42, which forms a first seat for bi-metallic means whose dimensions will vary according to its temperature. Preferably, the bimetallic means is in the form of a helical spring 43 of a bifilaric material whose other end engages a spring seat 44 provided at the other end of the rod 37. The bi-metallic means 43 consequently will be subjected to a change of shape dependent upon its temperature and in order to vary the temperature, it is surrounded by a heat winding, comprising a resistance wire coil 45 on a winding support 46. The resistance wire coil 45 in turn is electrically connected at 47 to a current source 48 and a thermistor 49. When the thermistor 49 is influenced by a change of temperature, the strength of the current created by the source of current 48 will also be changed. This current passes through the heater coil 45 with a consequent change of temperature and this change of temperature reacts in turn on the temperature of the bi-metallic means 43 which will either extend or contract in its axial direction. As the bi-metallic means 43 is rigidly supported at its one end against the bolt 41 and the disc 42, its other end, that is the end which engages the spring seat 44, will be displaced and this displacement will be transferred by the rod 37 to the thermostat 31. It will now be understood that both the reaction movement proper of the thermostat and the reaction movement of the bimetallic means 43 will cause a displacement of the valve body with the consequence that the function mentioned above in connection with FIGURES 1 and 2 is provided. A possibility for manual displacement in order to pre-set the valve exists by the cover 40 being connected to the cylindrical casing 39 by a threaded connection 50. If the cover 40 is turned in one or the other direction the cover, along with the bolt 41, will be displaced to a corresponding degree and will in turn cause an increase or decrease of the load on the bi-metallic means 43. When, in the above, the features of the present invention were described, details which are inessential to these principles (such as packings between the electrothermal motor 38 and the valve housing 36 and the fixture of the electro-thermal motor 38 to the valve housing 36) have been omitted for clarity. In FIGURE 3, arrows indicate the direction of movement of the water when the by-pass valve is used in a system according to FIGURE 2. The man skilled in the art will understand, from the above description, the movement of water when the valve is instead used in a system according to FIG URE 1. Double arrows in FIGURE 3 indicate movement of water from the return conduit 16, before this water has yet been distributed between the ports 27 and 28, whereas single arrows indicate the movement from the return conduit to each of the two ports 27 and 28.The movement from the port 26 to the port 27 is controlled by means of the valve opening between the valve body part 30 and its valve seat 29, whereas the movement from the port 26 to the port 28 is determined by means of a valve opening between a valve seat 51 on an intermediater wall 53 of the valve housing and a co-operating surface 52 on the valve body part 33. It will immediately be seen that the valve openings are closed and opened in counter time. WHAT WE CLAIM IS:

1. Control means for a heating system including a feeder conduit, a return conduit and a by-pass conduit for heat transfer medium, such as water, the control means comprising: a thermostatically controlled by-pass valve having a valve housing with three ports for connection of the valve to the by-pass conduit and in one of the feeder and

return conduits and a thermostat mechanically engaged with a valve body within the valve housing so that it can be influenced by the temperature of heat transfer medium in the valve to adjust the position of the valve body relative thereto and thereby vary the amount of medium passing through the by-pass conduit and/or said one of the feeder and return conduits; an electrothermal motor mechanically engaged with the thermostat and capable of adjusting the position of the thermostat and the valve body relative to the valve hosuing in accordance with the temperature of the motor; and electro-resistive means capable of sensing a change in a condition (e.g. temperature) of the environment around the sensing means and electrically connected to the motor to adjust the temperature thereof upon sensing said change.

2. Control means as claimed in claim 1 in which the electro-resistive means comprises a thermistor.

3. Control means as claimed in claim 2 which includes a power source between the motor and the thermistor.

4. Control means as claimed in any one of the preceding claims in which the electro-thermal motor comprises a heating element capable of transferring heat to means whose overall length varies on heating to adjust the position of the thermostat and the valve body.

5. Control means as claimed in claim 4 in which said adjustment means engages with the thermostat through rod means axially aligned with the valve body.

6. Control means as claimed in claim 4 or claim 5 in which said adjustment means comprises a bi-metallic spring member.

7. Control means as claimed in claim 6 in which said spring member comprises a helical spring.

8. Control means as claimed in any one of claims 4 to 7 in which said adjustment means is engaged with a first seat carried by a casing of the electro-thermal motor and with the thermostat.

9. Control means as claimed in any one of the preceding claims in which the force capable of being applied to the thermostat by the motor is manually adjustable.

1 0. Control means as claimed in claim 9 when dependent from claim 8 in which the motor casing comprises a cover supporting the first seat, the cover being axially advanceable relative to the remainder of the casing to adjust the position of the first seat and thereby manually adjust said force.

11. Control means as claimed in claim 4 or any claim dependent therefrom in which the motor comprises a tubular coil carrier on which the heating element is wound and which extends around said adjustment means.

12. Control means for a heating system substantially as herein described with reference to FIGURE 3 of the accompanying drawings.

13. A heating system including control means as claimed in any one of the preceding claims.

14. A heating system including control means as claimed in claim 1 and substantially as herein described with reference to FIGURE 1 of the accompanying drawings.

15. A heating system including control means as claimed in claim 1 and substantially as herein described with reference to FIGURE 2 of the accompanying drawings.