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.
--
Cheers,
Roger
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