adding room stat to qe2 programmer on gravity fed

1 Oct 2007
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United Kingdom

I am looking at adding a room stat onto out current programmer - the qe2.

Please can someone tell me if i will have any problems due to the fact that - as our system is very old - the heating and water are linked, and come on together.( You can only have the hot water on it own - or at least , thats how all the programmers weve had have always functioned!)

So, if the heating and water come on, and the stat turns it off, will the water stop heating too?


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With the type of system you have, turning on the hot water will turn on the boiler, the boiler heats the water which then circulates by gravity to the hot water storage cylinder above.

When you turn on the central heating, that switches on the pump which circulates the water around the radiators. The hot water has to be on at the same time to keep the boiler firing.

Adding a room thermostat is fairly easy, you wire it so that it switches off just the pump. As the boiler will still be operating, the hot water cylinder will still get hot water.

Here's a wiring diagram. (I have omitted the earth wire for clarity) Depending on the thermostat you buy, you may not need the earth or neutral connection.

Stem, thanks for the explination, it makes MUCH more sense how!

However, on that basis, fitting a room thermostat on this system for economical reasons would be irrelavent correct? as the boiler would still be firing even though the pump was off?
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Partially correct, but the boiler will consume less less gas than if the radiators were on unnecessarily.

Adding a thermostat will stop the house being overheated by the radiators and will make some saving. How much will depend on how well insulated your house is. Due to the mild weather, my thermostat in the hall set to 19 degrees, didn't even switch the radiators on at all this morning.

For maximum savings though you are right, an upgrade to full thermostatic control would be more energy efficient.

Here's a diagram showing how to incorporate a cylinder stat with changeover contacts. With this option the boiler will be turned off when both hot water and central heating are satisfied, but the boiler will be powered as required via the central heating circuit when the hot water is up to the set temperature.

In the summer when the heating is not selected it will turn off the boiler when the hot water is at the set temperature.


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