Thanx 4 ur reply. No, i don't have a multimeter. Feared this may b needed. I could just replace head. how is it attached? Do i need 2 drain down?
If the actuator, that's the box on top, has a small bump about 5mm across on the top, you can replace it without draining down. If not, then you have to replace the complete valve, which obviously means a drain down.
But before you rush out to buy a new valve or actuator, there are some simple tests you can do without a meter.
Turn CH and HW stats to min
Set programmer to CH and HW OFF
Turn off the electricity to the system.
Try moving the valve lever from Auto end to Man end. You should feel some resistance as you are opening the valve against a spring. Release the lever and it should move back to the Auto end with a whirring noise.
If the lever has no resistance or does not return, it's because the valve has stuck.
If the actuator is removable, take it off (remove cover - one screw, then undo two screws on opposite corners). This will allow access to the valve spindle ,which should turn easily by hand, but only about 20 degrees. You may need to use a pair of pliers if it is really stiff. Lubricate the spindle with some silicon lubricant, reassemble and test the system.
If the valve is sticking and you cannot remove the actuator, then it means a new valve and a drain down.
If the lever has resistance and returns, the fault is electrical
1. Turn CH and HW stats to min
2. Set programmer to CH and HW OFF
3. Turn off the electricity to the system.
(This resets the valve)
4. Turn HW ON
5. Turn HW stat to max -
Boiler should light
6. Turn power ON
The pipe from valve to cylinder should get hot; the pipe from valve to rads should stay cold
7. Turn HW stat to min -
Boiler should go out
8. Turn HW stat to max -
Boiler should light
9. Turn CH ON
10. Turn CH stat to max
both pipes from the valve should get hot
11. Turn the HW stat to min -
boiler should remain on (it may go out and come on almost immediately)
the pipe to the rads should stay hot and the pipe to the cylinder should cool down
12. Turn the HW stat back to max -
pipe to cylinder gets hot again
13. Turn the HW OFF at the programmer -
boiler should remain on (it may go out and come on almost immediately)
the pipe to the rads should stay hot and the pipe to the cylinder should cool down
14. Turn the CH stat to min -
boiler should go out
15. Check the valve lever - it should be loose as the valve is held in the CH open position.
16. Turn the power OFF
17. Check valve lever - it should have resistance as the valve has been reset.