In article ,
Andrew Gabriel wrote:
So basically I see it as a random instantaneous event, whose
probablity of happening increases over time as dust builds up.
I don't think you can meaningfully say "my boiler takes x years
to soot up".

Just to annoy IMM again, I checked my BE balanced flue boiler one year
after it was installed, and it was like new. So I sort of forgot about it.
Some *twelve* years later it sooted up without being touched in the
interim, and as you said it went from normal to sooted up in a couple of
days. A good clean, and it's been fine since.

I noticed the burning sound was different when it started to soot up, and
the inspection window showed some yellow on the flames, so my 'service'
consists of a regular visual and aural check.

--
*Honk if you love peace and quiet.

Dave Plowman London SW 12
RIP Acorn