Put the CH on yesterday for the first time and it won’t turn off. Its on a timer and supposed to be on twice a day, when its due to go off the light on the electronic valve goes out as normal but the heating keeps going. I’ve turned the main thermostat right down and its still going 🙁 Any ideas ?

Boiler type? Pic of valve?

See if there’s a squarish box on top of the pump. If thats **** the radiators may be bouncing off the walls when you’ve only got the hot water heating on. Thermostat won’t kick in if it’s that.

(I only know cos ours went)

The boiler is a Potterton ‘Prima F’ 2 seperate valves for CH and HW, both the same, ‘Myson Power Extra’ like this one…

If its two seperate two port valves, not a 3 port as shown. Then it’s the micro switch in the valve head that’s stuck/shorted and putting 240v down the orange wire

Do you hear the relay at the control box click off (or is it mechanical)?
Do you hear the motor try and turn on the three way valve?

We had this problem and I think it was something to do with one of the motorised valves. The boiler was waiting for a signal from the valve to turn off that it wasn’t getting.

Few links that perhaps support the theory:

http://www.theanswerbank.co.uk/Home-and-Garden/Question466680.html
http://home-diy-tips.co.uk/heating/pumps/thread277.html
http://www.ultimatehandyman.co.uk/forum1/central-heating-won-t-turn-on-motorised-valve-t23525.html

Really. It’s the microswitch in one of the heads. . 🙂

Yes, its two seperate two port valves, not a 3 port as shown.

I’ve just checked again and my ‘assistant’ has now ben relegated to other duties !! The light on the CH valve is not illuminated when its on, she was looking at the HW. Both of these were replaced in Sept ’02, is that about right ? As it sound as though the electrics are shot, is the electrical unit on top of the actual valve replaceable on its own or is it a complete unit with the valve ? If seperate, is it a job for an enthusiastic amateur,or one for someone not likely to flood the house ?

It’s playing with electrics, so not a job for an amateur.

The two oranges will need to come out of the wiring centre to confirm which one is sticking. There’s other checks that need to be done to confirm that there’s definitely no stray voltage on the demands.

Get a gas man in.

Edit:

No light on the valve might meem the lights broke, or there’s no power. I’d never use lights to fault find.

OK, will do, thanks.

I always use an apprentice to fault find / check the power is off……..