T i m wrote:
Hi all,

Mum has an old wall mounted, low capacity, b/f conventional gas boiler
and she's trying to keep it running till she revamps the kitchen.

It works fine (for what she needs anyway) but now and again the
overtemp stat trips, even though the main stat is set quite low and
I've never see it other than just 'ticking along'.

So, the (manually resetable) overtemp stat is of the remote type where
the copper sensor feeds though the outer casing to the heat exchanger
/ case and into a tube sitting inbetween the main boiler tubes.

I managed to find and fit what I as told (and it looked like) a new
old-stock replacement a while ago and whilst it seemed to help it
hasn't cured the problem completely.

So, can someone confirm that it is where it is to be able to measure
the temperature of the main boiler tubes (and cut the boiler out if
above a preset threshold), if there is a 'typical' reason why they
might trip and if it could be a false positive (tripping prematurely)


Typically they trip because the boiler is overheating. ;-)

That's usually going to be down to poor flow. Sludged pipes or failing pump
probably.

Tim