I recently replaced the motorised valve and the time controller for the system and although it works fine most of the time all too often the heating refuses to come on, with the room stat and the controller both calling for heat. Moving the lever on the motorised valve usually does the trick, but not always. Something I've noticed is that the valve motor housing is always quite hot, even when the boiler is not working.
Is it the valve, controller or something else?
Thanks for looking