Central heating not always coming on

[Kingdombuyer]

My central heating comes on when programmed am or pm. Boiler fires up, pump can be heard and radiators heat up as expected.

However, if CH alone is selected on control unit ( it lights up) but the boiler does not fire up, pump cannot be be heard and radiators remain cold. Moving temp up on hall thermostat makes no difference.
Once I select HW also on control unit, the heating then comes on....boiler fires up etc.

I suspect my control unit is faulty: Potterton EP2002.

Can anyone advise? ...thank you

 

[St0rmer66]

Sounds more like a sticking mid position valve to me, springs back to hot water fine (where it's been sat all summer not moving), able to move a bit to the mid position (when both are on) but too stiff for the motor to get it all the way over to CH only.

 

[Kingdombuyer]

"Sounds more like a sticking mid position valve to me"

Thanks for reply...how can I sort this...or does it need a new valve?