Hot water working but central heating wont work unless hot w

[Richard666]

I have an open vented central heating system. The hot water works but the heating dosn't. The motorised valve for the hating seems to work but the pump will only fire up if the hot water is on as well

 

[DeltaT2]

If you have two motorised valves, one for the HW & one for the CH? Then it sounds like a fault in your CH valve actuator head. The room thermostat powers up the synchron motor in the actuator head, but there is a micro switch that is engaged after the motor rotates, I think your micro switch is faulty mate, that being the case you need a new actuator valve head.

 

[MANDATE]

sounds more like a 3port mid position valve that's going to mid position but no further. or even if it does go to CH only, it don't light the boiler.
These have two micro switches any of which may be faulty and deltaT2s advice is best.
That's assuming the wiring was and is still correct.

 

[DeltaT2]

sounds more like a 3port mid position valve that's going to mid position but no further. or even if it does go to CH only, it don't light the boiler.
These have two micro switches any of which may be faulty and deltaT2s advice is best.
That's assuming the wiring was and is still correct.

Not too sure if it's a 'S' or a 'Y' mate?? The OP doesn't make it very clear.

Just for the craic, do you fancy a wee punt. I say it's an 'S' plan. £5 in a kids charity box if either one of us is wrong?...........

 

[Richard666]

Thanks a lot. As I have two motorised valves It sounds like I need a new actuator head. Any ideas how I replace one?