In an earlier contribution to this discussion,
Mike Lane wrote:

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

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.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!