Confused by thermostats

16 Sep 2011
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United Kingdom
I've just moved into a new built house (2-3 years old) and am trying to work out the heating system.

The ground floor has underfloor heating throughout and each room has a digital thermostat (Honeywell DT90E). However, these thermostats don't appear to be capable of activating the boiler. I have set a high temperature, so that the thermostat indicates that it is calling for heat (and I hear the switch click), but the boiler doesn't react.

On the first floor there's a basic dial thermostat which the boiler does react to. If this thermostat is set so that it is calling for heat I am then also able to control the temperature in the ground floor rooms using the digital thermostats. However, as soon as the temperature on the first floor reaches the level set on the dial the boiler switches off and I lose heating to the ground floor. As the upstairs thermostat is situated immediately above a radiator (the only one in the house without a TRV...) this happens pretty quickly!

It seems like the downstairs thermostats only control the flow to their respective rooms, while the upstairs one acts as a master and is the only one which has control over the boiler. I have to set the upstairs thermostat to a very high temperature so that the boiler is always on in order to have control over the ground floor temperatures.

Does this sound like a normal arrangement, or is it likely to be a fault or misconfiguration?

Would be very grateful for any advice.
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Typical of house builders.

It's been incorrectly installed. A thermostat should never be put near a radiator and definitely not above one.

The DT90E stats are only controlling the motorized valves for the U/F heating and rely on the upstairs stat to turn the boiler on.

What programmers/timers do you have?

Provided the motorized valves have auxiliary switches, you may be able to wire them up to control the boiler.

Unfortunately most house builders warranties don't cover the heating system after two years. However it might be worth contacting you local Building Control Dept and telling them about your problem.

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