Help, my central heating thermostat seems to have no effect

[dougsdir24]

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?

TIA

Doug

[The Natural Philosopher]

More likely a banged up motorised valve..

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

[mike ring]

[e-mail] wrote in news: [e-mail]:

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.

[Roger Mills (aka Set Square)]

A lot depends on what sort of system you've got. Have you got any motorised valves, and if so, how many and what type. [You're likely to have either a single 3-port valve (Y-Plan) or two 2-port valves (S-Plan)]

In particular with an S-Plan system, a fault can occur which keeps the heating on regardless of what the thermostat does. With this type of system, the room stat opens the CH zone valve and the cylinder stat opens the HW zone valve. The valves have independent switches on them which turn the boiler and pump on once they are open. So, if the stat tells a valve to close, but it jams open and fails to close, the heating stays on regardless. This *might* be your problem, but you need to tell us a bit more about what you've *actually* got.