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

wrote:
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?

More likely a banged up motorised valve..

You need to find the other end of that yellow wire..
TIA

Doug