GB2175996A - Heating installation control apparatus - Google Patents

Abstract

Control apparatus for a heating installation either of the fully pumped or semi-gravity type comprising a boiler thermostat, first timing means for setting periods during which heating of the hot water supply is effected under the control of the boiler thermostat, an air thermostat disposed in a region heated by radiator means, second timing means for setting periods during which the pump is driven under the control of the air thermostat to heat the radiator means and switching means for effecting, during periods when the first timing means are not operable to enable heating of the hot water in the hot water supply reservoir and the second timing means are operable to enable heating of said radiator means, heating of the boiler under the control of the air thermostat and continuous operation of the pump irrespective of whether the air thermostat is demanding supply of heated boiler water to the radiator means.

Description

SPECIFICATION Improvements in central heating systems This invention relates to heating installations and more particularly to control apparatus for operating such installations. Heating installations are either of the semi-gravity or fully pumped type.

The term, "semi-gravity operated heating installation" is used herein to describe a heating installation having a boiler, a hot water supply reservoir, pipe means extending within said reservoir in heat ex change relationship with water therein and con nected to the boiler, water circulation through said pipe means being effected by gravity attributable to thermal convection and radiator means connected in circuit with a pump and the boiler for forced circulation of hot water from the boiler through the radiator means.

By the term "fully pumped heating installations" employed herein, is meant a central heating system comprising a boiler connected by pump means with circuits respectively for supplying hot water from the boiler to the heating means, i.e. the tube coil of an indirectly heated hot water reservoir and for sup plying hot water from the boiler to radiator means for space heating purposes.

The usual electrical controls provided with a heating installation whether of the semi-gravity or fully pumped type, comprise a boiler thermostat for controlling the operation of the boiler firing mechan ism, a timing means for setting periods during which heating of the hot water supply is effected under the control of the boiler thermostat, an air thermostat disposed in a region to be heated by the radiator means and, optionally, a programmer. If the prog rammer is fitted it affords the alternative modes of operation where the installation provides either hot water only or hot water together with space heating during which the air thermostat controls the opera tion of the pump.If the programmer is not provided the air thermostat is manually turned down to a position well below ambient temperature to prevent space heating operation so that the option of hot water only is available during periods set by the timing means and hot water and space heating are available during the periods set by the timing means upon appropriate setting ofthe air thermostat. The option of space heating only is obviously not available. With these controls, the firing of the boiler during periods set by the timing means requires the temperature of the hot water supply to be main tained at a relatively high level. This is not necessary when the demand is for space heating only so that much wasteful boiler firing takes place.Further, the boiler thermostat reacts to switch on the boiler when the temperature of its water jacket falls because of cooling of adjacent pipes, the flue system and the boiler casing and this means that the boiler will fire wastefully from time to time after it has fully heated the hot water supply reservoir and the room space.

Although the primary control of the hot water temperature is the boiler's own thermostat, an additional thermostat is sometimes fitted for reasons of economy. This control is a hot water reservoir thermostat which is clamped to the side of the reservoir. When the temperature set on this thermostat has been achieved by water in the reservoir, the thermostat switches off the boiler.

Although the ability of the hot water reservoir thermostat to control hot water temperature is limited, it has the advantage of preventing continued firing of the boiler, attributable to boiler casing, adjacent pipe and flue losses, once the set water temperature has been reached. The provision of the reservoir thermostat also does not assist as regards having to run the boiler at a relatively high temperature when the demand is for space heating only, although to improve the effectiveness of the reser voirthermostat, it is often electrically interlocked with the air thermostat and the pump as well as the boiler firing mechanism.This ensures that should space heating be called for by the air thermostat after the hot water reservoir has reached its temperature set by the reservoir thermostat, the electrical circuit again enables the boiler to fire and the pump to operate for the duration of the call from the air thermostat.

Another possibility is afforded by the use of a reservoir thermostat. Rather than making the pump switch offwhen the airthermostat ceases to call for heat, the pump is allowed to continue to run and use in the radiators some of the residual boiler metal and water heat which would otherwise be lost through heat dissipation from the adjacent pipework and boiler casing of the system. In this arrangement it is important that the pump is stopped in the case of a semi-gravity system or prevented from supplying the radiators in a fully pumped system when the boiler has fired for hot water replenishment only otherwise unnecessary radiator heating occurs.

It is an object of the present invention to provide control apparatus for a heating installation which enables operation with reduced energy loss and with residual boiler heat extraction both without employing a hot water reservoir thermostat.

According to the present invention, control apparatus for a heating installation comprises a boiler thermostat, first timing means for setting periods during which heating of the hot water supply is effected under the control of the boiler thermostat to maintain the hot water supply temperature between predetermined limits, an air thermostat disposed in a region heated by the radiator means, second timing means for setting periods during which said pump is driven under the control of the air thermostat to maintain the temperature of the region heated by the radiator means between predetermined limits, and switching means effecting, during periods when the first timing means are not operable to enable heating of the hot water in the hot water supply reservoir and the second timing means are operable to enable heating of said radiator means, heating of the boiler under the control of the air thermostat and continuous operation of the pump irrespective of whether the air thermostat is demanding supply of heated boiler water to the radiator means.

In one form of the invention the heating installation is a semi-gravity operated installation so that when the first timing means is set for heating the hot water supply under the control of the boiler thermostat, heating of the hot water supply takes place by gravity attributable to thermal convection in the pipe means within the hot water supply reservoir.

In another form of the invention the heating installation is a fully pumped installation so that when the first timing means is set for heating the hot water supply under the control of the boiler thermostat, heating of the hot water supply takes place by the pump pumping hot water from the boiler through the pipe means within the hot water supply reservoir.

Suitably, during periods when the first timing means are not operable to enable heating of the hot water supply reservoir and the second timing means are operable to enable heating of the radiator means, the heating of the boiler is effected under control both of the air and boiler thermostats.

Advantageously, a hot water reservoir thermostat can be provided which operates in conjunction with the boilerthermostatto control the temperature of the hot water reservoir by switching off the boiler when the requisite reservoir temperature is achieved.

Suitably, where the first and second timing means are respectively operable to heat the hot water reservoir under the control of the reservoir and boiler thermostats and to fire the boiler under the control of the air and boiler thermostats, the action of the reservoir thermostat to switch off the boiler effects operation of the pump to reduce the boiler temperature and place the boiler thermostat in condition where it is calling for heat and thereby enabling control of the boiler firing under control of the air thermostat.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figures 1 and 2 are diagrammatic representations of two forms of fully pumped heating installations according to the invention, Figures 3 and 4 are circuit diagrams of control apparatus according to the invention for operating the installations respectively of Figures 1 and 2.

Figure 5 is a diagrammatic representation of a semi-gravity operated heating installation according to the invention, Figure 6 is a circuit diagram of control apparatus according to the invention for operating the installation of Figure land Figure 7 is a control panel for indicating the operating mode of the installations and circuits of Figures 1 to 5.

In Figures 1 to 4 like parts are denoted by the same reference numerals.

Referring to Figures 1 and 3, a fully pumped heating installation consists of a boiler 1, boiler thermostat 3, hot water cylinder or reservoir 5, tube coil means 7 extending within the reservoir in heat exchange relationship with water therein and connected to the boiler byway of a pump 11 and hot water zone valve 14 and radiators 9 connected in circuit with the pump 11 and a heating zone valve 12 and the boiler for forced circulation of hot water from the boiler through the radiators. Heating of water in the reservoir occurs by forced circulation in the circuit of the pump 11, hot water zone valve 14, tube coil means 7 and the boiler.First and second timing means 15 and 17 are provided which respectively are employed, in the case of timing means 15, to set the periods in the daily cycle during which heating of the boiler 1 is effected under the control of the boiler thermostat 3 to maintain the hot water temperature in the reservoir 5 between predetermined limits and, in the case of the second timing means 17, for setting periods in the daily cycle during which the pump 11 is driven under the control of an air thermostat 19 disposed in the region heated by the radiators 9. The timing means 15 consist of switch 21 actuated by a motorised clock (not shown) at preset intervals whilst the timing means 17 consist of switch 23 actuated by the motorised clock at preset intervals.

The first and second timing means and air thermostat 19 connect with the boiler thermostat and pump by switching means 25, the electrical circuit of these components being illustrated in Figure 3. The switch 21 ofthefirst or hotwatertiming means 15 is connected in series with an optional reservoirthermpstat 27 and the coil of a relay 29 between live and neutral connections 31, 33 of an electrical supply.

The relay 29 of the switching means 25 has three pairs 35,37 and 39 of switching contacts 41,43, 45, 47 and 49,51 with a three pole switch having actuating poles 53, 55 and 57 respectively for each contact pair.

In the embodiment of Figures 1 and 3, the solenoid of hot water valve 14 is connected in parallel with the coil of relay 29 and the end of that coil connected to the reservoir thermostat is also connected to contact 51 of switching contacts pair 39 and contact 47 of pair 37. The solenoid of heating valve 12 is connected between pole 53 of the pair 35 of switching contacts and neutral connection 33, contact 41 of the pair 35 being connected to contact 45 of contact pair 37 and also in series with switch 23 of the second timing means to the live connection 31 of the electrical supply whilst contact 43 of the pair 35 is connected to contact 49 of the pair 39.The motor of pump 11 is connected between the neutral connection 33 of the electrical supply and pole 55 of the pair 37 of relay switching contacts, contact 45 of which is connected in series with switch 23 to the live connection 31 of the supply whilst as already mentioned, contact 47 is connected to the same side of the coil of relay 29 as the reservoir thermostat.

The circuit of the boiler thermostat 3 is connected between the supply neutral connection 33 and the pole 57 of relay switching contacts pair 39, contact 51 of which is connected, as stated above to the same side of the relay coil as the reservoirthermostat whilst contact 49 of pair 39 is connected to the live connection 31 of the supply in series with the air thermostat 19 and the switch 23 of the second timing means.

Considering first operation in the hot water heating mode assuming the reservoir thermostat is calling for heat. Switch 21 and thermostat switch 27 are closed so that the coil of the relay 29 is energised and valve 14 has its solenoid energised so that the valve is open. With the relay coil energised the poles 53, 55 and 57 respectively engage contacts 43, 47 and 51 with the consequence that the boiler thermostat circuit is energised by way of switch 21, thermostat switch 27, contact 51 and pole 57 and the pump motor is energised by way of switches 21 and 27, contact 47 and pole 55.As the reservoir thermostat 27 is calling for heat, the boiler thermostat causes firing of the boiler until the reservoir thermostat is satisfied whereupon its switch opens, the solenoid of valve 14 is de-energised and that valve closes to prevent continued circulation through the heating coil 7 and the relay is de-energised so that the poles 53, 55 and 59 revert to contact with respective contacts 41,45 and 49. This results in de-energisation of the pump motor and boiler thermostat circuits. When the reservoir water temperature falls, as a result of heat loss to the atmosphere or hot water being drawn off and replaced by cold water, to the level set by the reservoir thermostat, the latter again calls for heat and the relay is again energised so that the valve 14 opens, the pump operates and the boiler thermostat circuit is energised.It will be noted that if the reservoir thermostat were to fail in the closed state thereof, the boiler thermostat would limit the temperature of water in the heating coil 7. It follows also from this that the reservoir thermostat is not essential.

If now the second timing means switches to its "on" mode, switch 23 closes. So long as the switches of the first timing means 15 and the reservoir thermostat 17 are closed, the relay is energised and, as explained above, the pump is energised by way of contact 47 and the boiler thermostat circuit is energised by way of contact 51.

The closure of switch 23 provided the air thermostat 19 is calling for heat and its switch is therefore closed, causes energisation of the solenoid of heat ing zone valve 12 by way of contact 43 so that the valve 12 opens and the pump circulates water from the boiler to the radiators 9. When the air thermostat 19 is satisfied, its switch opens and opens the circuit of the solenoid of valve 12 which thus closes. The pump motor however remains energised by way of contact 47, reservoir thermostat 27 and switch 21 of the first timing means and is effective to continue circulating water from the boiler through the coil 7 for heating water in the reservoir 5. When the air thermostat again calls for heat the valve 12 is again opened so that the pump circulates water from the boiler both through the coil 7 and the radiators 9.

Considering now the circumstances where the second timing means is in the "on" mode, the switch 23 thereof being therefore closed, and the air thermostat is calling for heat so that its switch is also closed. If either or both the first timing means switch 21 is open or reservoir thermostat 27 is satisfied and its switch therefore open, then the relay coil is de-energised as is the solenoid of the hot water zone valve 14. Also the poles 53, 55 and 57 revert to contact with respective contacts 41, 45 and 49 the effect of which is that the valve 12 is opened by reason of its solenoid being energised by way of pole 53, contact 41 and switch 23, the pump motor remains energised by way of pole 55, contact 45 and switch 23 and the boiler thermostat circuit remains energised by way of pole 57, contact 49, the air thermostat 19 and the switch 23.Accordingly, valve 14 prevents circulation in the coil 7 and the pump circulates water from the boiler only in the circuit of the radiators 9. Further, the firing of the boiler is under the control of the air thermostat 19. When the latter opens the boiler thermostat circuit is deenergised but the valve 12 remains open and the pump motor remains energised and water continues to circulate in the radiators and extracts heat from the stored heat of the boiler metal.

Turning now to the embodiment of Figures 2 and 4 the valves 12 and 14 are replaced by a single mid-position valve 60 which in a first position is set for water from the boiler to be pumped through the reservoir coil 7, in which position in the circuit of Figure 4 it is de-energised. In a second position valve 60 is set for circulation by the pump of water from the boiler through both the coil 7 and the radiators 9 and in a third position it is set for circulation of water from the boiler by the pump through only the radiator circuit.

In the circuit of Figure 4, the first timing means switch 21 and reservoir thermostat 17 are connected in series with one another and with the coil of relay 29 between the live and neutral connections 31 and 33 of the electrical supply. In the open position of switch 21 and/or reservoir thermostat 27, connection is made with the solenoid means of valve 60 to energise the solenoid by way of lines 62 and 64 from the live and neutral connections of the supply. A further line 66 connects from valve 60 to pole 53, the associated contact 41 of which connects to the live side of the electrical supply by way of switch 23 of the second timing means 17 whilst the other contact 43 associated with pole 53 connects with the live side of the supply via the series arrangement of air thermostat 19 and switch 23.The motor of pump 11 is connected at one side to the neutral side of the supply and at the other side to the pole 55 which connects either with contact 45 or contact 47, contact 45 going to the live connection 31 of the supply by way of switch 23 and contact 47 going directly to the supply connection 31. The boiler thermostat circuit at one end thereof goes to the neutral supply connection 33 and at the other end to the pole 57 which engages with one or other of contacts 49 and 51. Contact 49 connects both with contact 43 and with the live connection of the supply by way of air thermostat 19 and switch 23 whilst contact 51 connects directly with the supply live connection 31.

Considering first operation with the first timing means in the "on" mode, i.e. switch 21 closed, and the reservoir thermostat 27 calling for heat, the second timing means being in the "off" mode, i.e.

switch 23 open. In these circumstances, the relay coil is energised and poles 53, 55 and 59 are engaged with respective contacts 43, 47 and 51. The pump motor is therefore energised because of engagement of pole 55 with contact 47 and the boiler thermostat circuit is energised because of engagement of pole 57 with contact 51. Valve 60 is de-energised and therefore in the disposition where it allows pumped water from the boiler to circulate through the reservoir heating coil 7. The hot water heating is therefore under the control of the reser voirthermostat and when the latter opens, the boiler thermostat circuit and pump motor circuit are deenergised and the valve 60 is energised via switch 21 and lines 62 and 64 and circulation of water from the boiler in the coil 7 is prevented.As with the circuit of Figure 3 it will be apparent that as opening of either the switch 21 or the reservoir thermostat de energisesthe relay, the provision of the reservoir thermostat is not an essential and in its absence the hot water heating would be under the control of the boiler thermostat.

Considering now the condition where the first and second timing means are in the "on" mode i.e.

switches 21 and 23 are closed and the switches of the air reservoir thermostats 19 and 27 are closed i.e.

these thermostats are calling for heat. Again, the relay coil is energised and the poles 53, 55 and 57 engage respectively contacts 43,47 and 51 so that the pump and boiler thermostat circuits are energised as before. The effect of the closure of switch 23 and the air thermostat switch is that valve 60 is energised via neutral line 33, line 64, line 66, pole 53 contact 43, the airthermostat 19 and switch 23 and the valve 60 in consequence is disposed to afford circulation of water from the boiler by the pump both through the reservoir coil 7 and the radiators 9.

When the air thermostat is satisfied and its switch opens, the solenoid of the valve 60 reverts to its de-energised state and, in that condition thereof, the pump can only circulate water from the boiler through the reservoir coil 7 and not through the radiator circuit. The operation then proceeds as described above for hot water heating i.e. with the switch 21 closed and the reservoir thermostat calling for heat. Opening then of the reservoir thermostat has the effect previously described.

If the second timing means is in the "on" mode and the air thermostat is calling for heat and further the first timing means is in the "off" mode, the valve 60 is energised by way of lines 62 and 64 and also, as switch 23 is closed and pole 53 is engaged with contact 41, by way of lines 66 and 64. With this form of energisation, the valve is set for circulation of water from the boiler by the pump to the radiators 9 only and not to the reservoir heating coil 7. The pump is energised by reason of engagement between pole 55 and contact 45 and the closed state of switch 23 whilst the boiler thermostat circuit is energised because pole 57 is closed on contact 49 and is in series with the air thermostat switch and switch 23 which are both closed. Thus the boiler is under the control of the air thermostat and when the switch of the latter opens the boiler thermostat circuit is de-energised.However, opening of the air thermostat switch does not effect the pump which continues to circulate water from the boiler to the radiator thus using the heat in the boiler metal.

Accordingly, in the embodiments of both Figures 1 and 3 and Figures 2 and 4 at times when the second timing means is in the "on" mode and the first timing means is in the "off" mode, the pump runs continuously and the boiler is under the control of the airthermostat. Also in this mode of operation if the boiler thermostat is not calling for heat, the pump circulates water from the boiler to the radiators until the boiler water temperatures falls to the level where the boiler thermostat calls for heat and thereafter the boiler is switched on and off by the action of the air thermostat.

Referring now to Figures 5 and 6, a semi-gravity operated heating installation consists of a boiler 100, boiler thermostat 300, hot water, cylinder or reservoir 500, pipe means 700 extending within the reservoir in heat exchange relationship with water therein and connected to the boiler and radiators 900 connected in known manner in circuit with a pump 110 and the boiler for forced circulation of hot water from the boiler through the radiators. Heating of water in the reservoir occurs by gravity as a result of thermal convection giving rise to water circulation in the circuit of the pipe means and the boiler.First and second timing means 130 and 150 are provided which respectively are employed, in the case of timing means 130, to set the periods in the daily cycle during which heating of the boiler 100 is effected under the control of the boiler thermostat 300 to maintain the hot water temperature in the reservoir 500 between predetermined limits and, in the case of the second timing means 150, for setting periods in the daily cycle during which the pump 110 is driven under the control of an air thermostat 170 disposed in the region heated by the radiators 900.

The first and second timing means and air thermostat connect with the boiler thermostat and pump by switching means 190, the electrical circuit of these components being illustrated in Figure 2. In this circuit the timing means 130 and 150 are represented has simple on/off switches. The first or hotwater timing means 130 is connected in series with the coil of a relay 210 between live and neutral connections 230, 250 of an electrical supply 270. The relay 210 of the switching means 190 has two pairs 290, 310 of switching contacts 330,350 and 370, 390 with a double pole switch having actuating elements 410 and 430.

The second or space heating timing means 150 is connected between the live and neutral contacts of the supply 270 in series with contact 350 of pair 290 and, by way of switch element 410, pump 110. Also connected to contact 350 is one side of the air thermostat 170 of which the other side is connected to the other contact 330 of the pair 290 and one contact 370 of the pair 310, the other contact 390 of pair 310 being connected to the live terminal 230.

The element 430 connects by way of the boiler thermostat 300 with the neutral termnal 250 of the supply.

In the mode of operation where the first timing means is in the "on" condition, the switch thereof indicated by reference 130 is closed and relay 210 is energised. This effects closing of the double pole switch elements 410 and 430 respectively with contact 330 of pair 290 and contact 390 of pair 310.

The boiler thermostat is thus placed in series with switch element 430 and contact 390 and the supply 270. Accordingly, the boiler is switched on and off by the boiler thermostat to control the hot water temperature of reservoir 500 between predetermined limits.

When during a period that the switch of the first timing means is closed, the switch of the second timing means 150 is also closed, the relay 210 is unaffected by such closure and elements 410 and 430 remain closed with contacts 330 and 390.

However, the switch of the second timing means 150 is placed in series with the air thermostat 170, the contact 330, switch element 410 and the pump 110 so that the pump is switched on and off by the air thermostat 170 whilst the boiler remains under the control of the boiler thermostat.

In the operational mode where the second timing means 150 is in the "on" condition whilst the first timing means is in the "off" condition, the relay 210 is de-energised so that the switch elements 410 and 430 are engaged with contacts 350 and 370. The pump 110 is thus connected to the supply by way of switch elements 410, contact 350 and the second timing means 150 and runs continuously whilst the second timing means is also placed across the supply in series with the air thermostat 170, the boiler thermostat 300, the switch element 430 and contact 370 so that firing of the boiler is responsive to closure of the contacts of the air thermostat 170 provided the hot water temperature is such that the boiler thermostat is also calling for heat.If the heater thermostat is not calling for heat the pump will circulate water thus lowering the boiler water temperature until the boiler thermostat is in a condition where it calls for heat whereupon the boiler is fired on and off by the action of the air thermostat.

In the case of each of the embodiments of the invention described, by allowing the boiler to fire only when the air thermostat calls for heat, assuming the boiler thermostat is also calling for heat, and then allowing the pump to operate continuously the boiler water is substantially cooled. On a further call from the air thermostat water is heated only to a level necessary to satisfy the further requirements of the airthermostat. This call may well be met with a level of water temperature much lower than the normal operating temperature of the boiler. Lower boiler water temperatures makes for improved efficiency due to lower boiler casing and flue losses and the improved ability to transfer heat from the combustion gases.In conventional systems, wasteful temperature overshoots occur because of pulsing of high temperature water through the radiators whenever the air thermostat calls for heat.

With the described embodiments of the invention it becomes possible to set the second timing means for earlier turn off due to the delivery of hot water to the radiators right up to the last moment of the "on" time.

The described embodiments of the invention also encourage parallel heating of radiators and hot water. In cold weather, the first or hot water timing means may be switched off altogether and all hot water heating achieved as a consequence of necessary space heating runs. It will be remembered that with a conventional system the boiler will often fire to produce hot water only. Because of the relatively slow transfer of heat to the hot water reservoir, this means high boiler water temperature persists with consequent decrease in efficiency.

Referring to Figure 7, control panel 470 illustrated therein incorporates different coloured lamps 490 and 510 respectively illuminated when the first and second timing means are in the "on"mode. The lamps are high resistance devices 530 and 550 in series with switch contacts 570 and 590 closed by single pole elements 610 and 630 which form double pole elements with the switch elements of the first and second timing means 130 and 150 and operate therefore in unison therewith. Accordingly the mode of operation of the installation, that is to say whether it is in the "hot water heating only" or the "space heating" or the "hot water and space heating" mode can be ascertained simply by inspection. Although the lamp devices 530 and 550 are illustrated only in the circuit of Figure 6 they could equally well be present together with their associated switch poles and contacts in the circuits of Figures 3 and 4.

Those skilled in the art will appreciate that a reservoir thermostat disposed in series with the first timing means 130 of Figure 7 can be employed in the same way as is the reservoir thermostat in the circuits of Figures 3 and 4.

Claims (10)

1. Control apparatus for a heating installation having a boiler, a hot water supply reservoir, pipe means extending within said reservoir in heat exchange relationship with water therein and connected to the boiler and radiator means connected in circuit with a pump and the boiler for forced circulation of hot water from the boiler through the radiator means, said control means comprising a boiler thermostat, first timing means for setting periods during which heating of the hot water supply is effected under the control of the boiler thermostat to maintain the hot water supply temperature between predetermined limits, an air thermostat disposed in a region heated by the radiator means, second timing means for setting periods during which said pump is driven under the control of the air thermostat to maintain the temperature of the region heated by the radiator means between predetermined limits, and switching means for effecting, during periods when the first timing means are not operable to enable heating of the hot water in the hot water supply reservoir and the second timing means are operable to enable heating of said radiator means, heating of the boiler under the control of the air thermostat and continuous operation of the pump irrespective of whether the air thermostat is demanding supply of heated boiler water and the radiator means.

2. Control apparatus as claimed in Claim 1,wherein heating of the boiler under the control of the air thermostat during periods when the first timing means are not operable to effect heating of the hot water supply reservoir and the second timing means are operable to enable heating of the radiator means is effected by the switching means placing the air thermostat and the boiler thermostat in series across the electrical supply so that heating of the boiler under the control of the air thermostat occurs only in circumstances where the boiler thermostat is not calling for heat.

3. Control apparatus as claimed in Claim 1 or Claim 2, wherein a hot water reservoir thermostat is provided which operates in conjunction with the boiler thermostat to control the temperature of the hot water reservoir by switching off the boiler when the requisite reservoir temperature is achieved.

4. Control apparatus as claimed in Claim 3, wherein the first and second timing means are respectively operable to heat the hot water reservoir under the control of the reservoir and boiler thermostats and to fire the boiler underthe control of the air and boiler thermostat, the action of the reservoir thermostat to switch off the boiler effects operation of the pump to reduce the boiler temperature and place the boiler thermostat in condition where it is calling for heat and thereby enabling control of the boiler firing under control of the air thermostat.

5. Control apparatus as claimed in any preceding claim, wherein the heating installation in a semigravity operated installation so that when the first timing means is set for heating the hot water supply under the control of the boiler thermostat, heating of the hot water takes place by gravity attributable to thermal convection in the pipe means within the hot water supply reservoir.

6. Control apparatus as claimed in any one of Claims 1 to 5,wherein the heating installation is fully pumped installation so that when the first timing means is set for heating the hot water supply under the control of the boiler thermostat, heating of the hot water supply takes place by the pump pumping water from the boiler through the pipe means within the hot water supply reservoir.

7. Control apparatus as claimed in Claim 6, wherein a first solenoid operated valve connects the pipe means for heating water in the hot water supply reservoir in a circuit with the pump and the boiler and a second solenoid operated valve connects the radiators in a circuit with the pump and the boiler.

8. Control apparatus as claimed in Claim 6, wherein a mid-position valve is connected with the boiler, the pump, the pipe means in the hot water supply reservoir and the radiator means and has three operative positions in a first position of which pumping of water by the pump solely through the pipe means in the hot water supply reservoir is enabled, in a second position of which pumping of water by the pump through both the radiators and the pipe means in the hot water supply reservoir is enabled and in the third position of which pumping of water solely through the radiators is enabled.

9. Control apparatus as claimed in any preceding claim, wherein there is provided a control panel having indicating means for registering respective operational modes when heating of hot water only, heating of both hot water and radiators or heating solely of radiators is taking place.

10. Control apparatusfora heating installation substantially as hereinbefore described with reference to any one of the embodiments shown in Figure 1 and 3,2 and 4 or 5 and 6 of the accompanying drawings.