Central Heating will not switch off

[DurantUK]

Hi,
My Central heating will not switch off (hot water seems to work normally).
The heating stays on despite being turned to cold on the thermostat and off at the controller.
I think I may have tracked the problem to the Meyson MPE 222 Power Extra valve, when the heating sticks on there is no resistance in the return spring if I slide it to manual. If I slide it back and forth between auto and manual eventually the spring responds and pushes the lever back to auto then the central heating works fine and obeys the thermostat and controller? (for a while).
Any suggestions if this may the valve or the actuator?
Boiler is a Potterton Suprima HE and the system is a sealed system with an expansion vessel.
Thanks

 

[Simon F]

Hello Durant, welcome along.
sounds like you have diagnosed the issue, motorised valves are the usual culprit with electrical supply problems.
if the motor was at fault the valve would fail to properly open.
the fact that it opens and stays open suggests its sticking inside, time for a complete new valve

 

[DurantUK]

Thanks for the advice, it's greatly appreciated