Central heating not switching off

[langtounboy]

System is a fully pumped y plan system. Potterton boiler.
There is no problem with the DHW.
However the central heating will not switch off, the radiators are continually hot, room thermostat makes no difference, switching CH off on the controller no difference.
Only way to switch it off, is to switch off the DHW and CH together.
I thought, 3 port selector valver, I took the cover off and selected the DHW CH etc and the actuator did move.
I'm still thinking its this valve but before I drain the system has anyone got a better idea?

 

[kevplumb]

sticking / stuck microswitch in the valve actuator

 

[twgas]

Valve letting by
Turn whole system off and allow to cool, once cool turn on hot water only, feel feed to CH if it gets hot a new valve reqd.

 

[langtounboy]

Ended up having to change the entire valve, I was hoping to just change the actuator but the valve and actuator were a combined unit

This seems to have fixed the problem, thanks for the help