"Zax" wrote in message
...

"John" wrote in message
...

"Zax" wrote in message
...
have a 20 year old boiler- gravity flow, pilot light, with a hot water
cylinder in the airing cupboard.
recently (a week ago) had a plumber drain the boiler to sort out
problems
with radiators (also fitting thermostatic valves all over the house on
the radiators).
since then (maybe coincidentally?) the boiler is misbehaving.
on manually lighting it, the pilot comes on, the boiler fires up, can
see
the flames clearly, then the flames gutter and go out. (i can see a lot
of yellow flames- is that unusual? i thought they would be all blue.)
after repeated attempts, the boiler stays on when left on a continous
timer setting. leaving it on a twice a day setting, the pilot goes out
and the boiler does not heat up.
what could the possible problems be? is the boiler kaput?
any help appreciated.

If you told us what make and model of boiler it is we might be able to
make a sensible contribution. Also when was the boiler last serviced and
is all ventilation clear?

its a glow-worm balanced flue boiler 100B
last serviced 2 years ago
all ventilation clear.



If it's a Glow Worm balanced flue 100B (like mine) and the flames are all
yellow, the heat exchanger fins are all blocked up with soot. This is
marginally dangerous as there will be partial combustion and poisonous fumes
(but only marginal as it's a balanced flue and they all go outside.

It is possible to do it DIY (I've just done mine) but I cannot recommend
this to anyone for obvious reasons. It MUST be done, however. Whoever does
it has to remove all the internal covers and laboriously clean between the
fins (lolly sticks just fit between them, and a stiff paint brush). The
stuff that comes out is ultrafine carbon, the dirtiest substance known to
man. You are in for a right pasting from SWMBO (probably). Don't use the
best vacuum cleaner (I did - once { ).

As an aside they ususally last 5 years before sooting up (this is my one's
second event). This means the "service" you had was the usual quick hoover
round and didn't involve cleaning the heat exchanger properly.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)