Conventional vented fully pumped system with motorised valves to CH & DHW. Still set to come on for a couple of hrs am & pm. Mainly for dhw but ch just in case. Came home this afternoon and heating is running flat out. Way over roomstat temp setting. I presume this is likely a failed microswitch in the CH valve. Will check.
Otherwise, any likely culprits please?
Nick.
Or stuck room stat.
The valve may be stuck open, which will close the micro switch. Check by moving the manual lever usually used while venting the system. You should be able to feel the resistance as you move the valve if it isn't stuck open.
The microswitch is supposed to close when the valve is fully open - and then switches on the boiler and pump.
If the switch stuck in closed position without the valve being open, the boiler and pump would run, but the radiators wouldn't get hot because the valve would be closed. The water would just circulate round the by-pass circuit.
For the heating to be on, the valve must be *open* - either mechanically stuck in the open position, or being told to open by a duff roomstat.
This happened to me. The valve needed to be worked back and forth several times with the motor removed, then it worked fine. I think it just wanted some attention, rather like the cat.
Many thanks to all. Checked stat and that is doing what it should. Davey hit this one on the head. Tried the lever on the valve and it was 'sticky'. Set valve to manual open and removed the motorhead. Valve stem rotated quite freely. Worked the valve a few times and it returned to close, as it should. Reassembled and now working ok. This weekend I'll have it off, the head, and see if I can clean/lubricate. Probably change the motor whilst doing so. Trouble is that it is beneath floorboards in a kitchen cupboard.
Again, thanks to all, Nick.
Glad it's working. They have, by law, to be in the most awkward place for access.
Hoping not to tempt fate, but mine is still working after at least two years now since the event.
Nothing wrong with having it off at the weekend and getting a bit of head to boot..............:-)
Not forgetting the all-important 'clean/lubricate'.
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