Heating pipes under floor interferring with thermostat?

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I recently replaced a simple analogue 3 wire thermostat with a Horstmann Centaurstat 7 to enable us to prevent the house getting too cold at night and also to have the heating coming on at different times on different days as the original controller didn't allow this. The new thermostat was fitted in the same position as the original.

The new thermostat is working correctly. However, it has a current temperature readout on the display and we've noticed that the temperature reading doesn't change when the house feels cold and we'd expect the heating to come on. Obviously because it's new we watch this like a hawk as we didn't have this feature before!

I've subsequently noticed that there are some central heating pipes buried under the tile floor that pass very close to the wall where the thermostat is mounted. When the heating has been on for a while the floor heats up and there is an underfloor heating effect in the localised area of the pipes. The hall is quite large but there is approximately 2 square meters of floor that gets warm which is pretty much directly under the thermostat.

Would i be right in thinking that this will be reducing the sensitivity of the thermostat as the floor acts as a heatsink and prevents the thermostat from seeing the true air temperature? Presumably when the heating is coming on from cold it won't be an issue as the floor will not be radiating, but once the section of floor with pipes underneath it has warmed up this will be radiating heat and therefore stopping the thermostat from seeing the true temperature in the hall.

Comments appreciated.

 

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In milder weather the radiators may go completely cold because the room temperature is at the temperature set on the thermostat. Although the air temperature is correct, you feel cooler because there is no radiant heat from the radiators. The same effect occurs if you are in a room and the sun comes out and shines in though the window, you immediately feel warmer because of the radiant heat, however, the actual air temperature won't have changed.

I think it is unlikely that the thermostat is being overly effected by the pipes under the floor especially if they are connected to the central heating that is controlled by the said thermostat and will go off when the temperature is reached. Also if they were there with the previous thermostat and it wasn't a problem it seems unlikely. Does this part of the room feel significantly warmer that the rest of the room?

It's also possible that your new thermostat is responding more quickly to the temperature change, whereas your older one was overheating a bit.

Regardless, of the above, it would be a good idea to lag the pipes anyway. If some heat is escaping from them upwards, there will also be some being lost below. For a hours work, and a bit of pipe insulation it would be well worth it.

You can check the thermostat by hanging a thermometer from it and seeing if the set temperature is maintained. (sometimes there can be a discrepancy of a degree but is should be a consistent discrepancy)

My guess is that when we hit winter properly and the radiators never go completely cold before coming on again you won't notice it.

 

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Thanks for the reply. Good point about the radiant heat compared to air temperature.

The pipes are buried in a tiled, solid floor so no option to lag them. As i said, this gives an underfloor heating effect where the floor around the pipes stays warm much longer than the radiators. This area of the hall does feel warmer underfoot but i've no idea on the air temperature. As this area of floor is directly under the thermostat i wondered if it would have much impact.