In article <_
ZKdndTZ65ZR7T7K...@brightview.co.uk>,
This means the channels up through the heat exchanger are blocked.
Almost certainly nothing wrong with the gas valve or burners.
First thing, you need to get a different Gas Safe engineer (or CORGI
in Northern Ireland). The one you have is incompetent - he has
wrongly diagnosed the problem, and should have disconnected the boiler
as unsafe.
You said there was a fall of soot - where from?
You probably need to get the chimney swept before cleaning boiler.
Then you need to get the boiler serviced by someone who knows what
they're doing. This involves removing the burners and getting access
to the combustion channels and using a stiff brush to brush out all
the soot, being careful not to knock off too many of the heat
exchanger nipples. (Brushes are sized and shaped to fit channels in
different boilers.) Use mirrors and lights to ensure the channels
are completely clear of soot. Then the burners need soot and dust
cleaning out, and ensuring jet(s) and mixer tubes are clear (might
be one for all of them, or one per burner, depending on design).
If the boiler is running properly, no soot is formed. In normal
operation, a small amount of solid debris forms (burned dust, flies,
etc) inside the heat exchanger. This falls off and can get into the
burner air intake (together with dust). As the air intake gets
restricted by dirt, the flames will start to generate soot, and this
drops back and rapidly makes the situation worse. Within a couple of
weeks, the effect will "run-away" rapidly generating more soot, which
rapidly makes it worse until it's ended up in the state yours is in.
It's an open-flued boiler and extremely dangerous to use in this
state, as it will be generating carbon monoxide in addition to soot.
This type of boiler really does need an annual check, and you should
have carbon monoxide detectors fitted and tested at the same time.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]