In article ,
Paul Barker writes:
A neighbour asked me to help him as his boiler wouldn't light the other
day. The boiler was ancient Can't recall the make but it was basically a
multipoint style of heat exchanger with the cooling veins of 15mm pipe
running through. A previous fitter had shorted out the oh stat (most
likely because parts were unobtainium) and told them to leave the temp
control where it is (though the user had forgotten exactly where that
"where it is" was. He had taped the whole thing together with closure
plate tape.

For a description of what happens when one of these
overheats, see "The Self-Uninstalling Gas Water Heater"
http://www.diyfaq.org.uk/humour.html#uninstalling

This was a 1970's model and didn't have the overheat
stat. The 2000 one which replaced it did (and it's a
bog standard electrical component, so easily replacable
if needs be).

--
Andrew Gabriel