room thermostat overides central heating controls

[anthonyj]

have replaced both motorised valves on my s plan central heating, but room thermostat temperature overides controls, so c/h comes on when thermostat increased even if programmer is off or in timed but off. Seems like could be a wiring fault but there are only 2 wires from honeywell box to thermostat.
any ideas please

 

[aesmith]

You need to follow the wiring from the programmer. CH On from the programmer should go to one side of the thermostat, then the other side should go to the heating valve.

Can you provide more information about how everything's connected?

 

[stem]

It's not unknown for the contacts inside a programmer to weld together and provide a permanent live supply to the thermostat regardless of the selected mode. This normally occurs if there has been a short circuit somewhere.

Have any of the fuses associated with the heating / boiler blown recently?

Has this problem always been there, or has it only recently occurred? If it's recent was anything changed, or altered prior to the fault occurring?