My system has started playing up. We noticed it when the weather turned warmer, and we turned the heating off. But the heating stays on regardless even if we also switch the water off at the timer (a Honeywell 7 day water and heating model). Basically, the pump continues working and the boiler fires up. The only way I can get things to stop is to turn the timer off at the mains. I have disconnected the frost stat to no avail, so that can't be the problem.
Any help would be appreciated. Thanks
Look back to the 27th, post in capital letters. Same problem.
The most likely diagnosis is that you have a zone valve which is either stuck open - even when turned off at the programmer - or the micro-switch, which provides its auxilliary contacts, has failed shut. [I am assuming that you have an S-Plan system, with separate 2-port valves for HW and CH rather than a Y-Plan system with a single 3-port valve?]
Someone else reported a similar problem recently which turned out to be a failed pump over-run stat on the boiler. I have to admit that I'm struggling to understand how this would make the boiler fire - rather than just running the pump continuously - but it's nevertheless something else to check.
My Dad had a seized 2 port valve on the supply to the cylinder coil recently - try fiddling with the manual override lever on the side, if you do have such valves in your setup - it should be fairly clear if you can actuate the valve or not. Best to turn the boiler electricity off at the fuse in case the housing cover falls off (they do sometimes) and you stick your fingers accidently into something live...
HTH
Tim
Motorised valve jammed.
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