Room thermostat not turning off the heating

Hi - im trying to work out a problem with my central heating, the room thermostat (drayton RTS1) doesent switch off the heating, even if i turn it right down it has no effect. I can hear it clicking as it you turn it up and down but the heating remains on. I have tried replacing the room stat with the a new one - same make and model and the problem persists. The programmer is a Horstman C21 which replaced a Drayton LP241 about 2 years ok. It is a pumped system. I have noticed that if I remove the programmer from the wall completely and then replace it, it works for a while and then goes back to the same problem, I have checked the connections on the wiring and the contacts and i dont think this is the problem. My next thought is to try replacing the programmer but I was looking to see if anyone had any other thoughts before I spend my money.

Thanks

Replacing the horstman with a decent brand would not be a bad idea.

should be easy to fix


first you need to make sure you have 240V from your time clock CH ON to the roomstat then from your room stat (when stat is calling for heat) to the brown wire of the CH zone valve and you should now have 240 on grey or the orange wire of the zone valve (one of these will be to permanent live so will always have 240v and the other being the one to fire the boiler (switched live)

now with the heating demand off at the thermostat you should have 240 into your stat and 0v out of the stat leaving 0v to your brown wire and leaving 0v to either the orange or grey (depends on installers preference)

i think you will find in any circumstance you will have 240v on either grey or orange whicj indicates valve is stuck open and operating end switch permanently


hope this helps and isnt to confusing never was any good at writing descriptions

Should be easier than that

Microswitch sticking in an MV gets my vote.

Gents - thanks for all your ideas - I think i follow you with the wiring but im no electrician - I have a multimeter and the house is on circut breakers so i will have a fiddle and see if I can check the voltage without giving myself a shock!

Assuming one of the suggestions is correct and its either the micro switch or the valve - where do I find them - are we talking the gas valve inside the boiler?

View media item 11149 micro switch is inside the head