Thanks for your help on this a friend has a multi meter i can borrow but i think your right that it is the micro switch which will mean i will have to purchase the whole actuator as against just changing the motor .
I have checked the stat and this is working .A friend suggested this problem could be the motorised valve so i have changed the motor in the actuator but has not made any difference,I get heat to the rads if i select heating on the actuator . my system is a conventional gravity fed system with a...