In an earlier contribution to this discussion,
Roger Mills wrote:

In an earlier contribution to this discussion,
Dave Osborne wrote:


Graham, you can use a Manrose 1351 bathroom extractor fan timer. We
will be publishing a wiring diagram for this application on the wiki
in the next day or so. Watch out here for the announcement from me or
John Rumm.
I'm told this is the Manrose 1351 although it doesn't say so anywhere
in the description: -

http://www.tlc-direct.co.uk/Products/BGDT20.html

Cheers,
DaveyOz

Indeed - I use one of these for just this purpose. It's slightly
fiddly to adjust the delay - a little to screw to turn, covering a
range of 1-45 (or is it 60?) minutes. It's best to adjust it on the
bench, switching (say) a light bulb off - and fiddle until you get
the desired delay. It seems fairly consistent once set. Mine is set
to about 4 minutes - which seems to be enough to stop the boiler
overheating under the circumstances which the OP described.


An afterthought for Graham. . . . If the pump keeps going after the boiler
stops, the water *does* have somewhere to go, doesn't it? This is not always
the case! For example, on S-Plan systems, the motorised valves will all be
closed in these circumstances, so there needs to be a bi-pass circuit -
preferably using an automatic bi-pass valve.
--
Cheers,
Roger
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