DIYbanter - View Single Post - Help, my central heating thermostat seems to have no effect

wrote in
oups.com:

I thought my old dial thermostat wasnt working as my heating would be
on full blast, even when the thermostat was set to 10 degrees.
So u purchased a digital one but this one seems to be the same too.
According to the new thermostat, the house temperature was 26 degrees,
the program was set to knock the heating off at 20 degrees but the
heating remained on.
I dont think its my wiring, i think it might be a problem at the other
end of the wiring but im not sure where that cable goes.
I wired the red cable into COM and the Yellow cable into NO.
Could this be a problem at my boiler?

Take the thermostat off; switch on the heating-remember the wires are live;
if the radiators heat it's definitely not the thermostat, put it back and
forget it. (you'll be very glad you got it once the problem is sorted)

The thread after message 574590 will help on wiring.

I assume you also have a hot water cylinder stat; if so wind the room stat
and the cylinder stat right down and see if the boiler stops (any timers to
24hrs on).

If it doesn't you probably have a wiring problem, or the 3 position valve
or CH zone valve is faulty and calling the heating all the time.

The valve may be stuck - take off the electric bit on top (with a bit of
luck it will detach easily and leave the valve behind, and check if the
valve works fairly easily.

I'm always a bit nervous posting here, the experts can jump on your neck,
so see how you get on with that and call back.

--

mike