I'm sure I know what the answer will be before I ask, but..

I have a Potterton Suprima 30 b/f boiler which has an intermittent
firing problem. The boiler does not fire up, either on start or when
heat is demanded. The pump is circulating, but it appears that the
fan which kicks in before the ignition fires doesn't start.

The problem seems to occur in fits and starts; it can be months
between occurrences, but when it happens it happens several times over
a number of days, but not all the time. Normally a press of the Reset
button will fire it up, but over the last few days, it's not always
worked first time.

The PCB was replaced in 1999, when the boiler was a couple of years
old, and the problem didn't re-occur until last year. Looking at it
today, the PCB looked fine to the naked eye (no obvious arcs or dry
solder joints), as did the wiring with the exception of the HT lead to
the ignition, which was ever so slightly frayed. I don't think this
is the problem; the boiler appears to ignite OK, it's the
preliminaries which seem to be the problem.

Any ideas? Is it time to replace the PCB again?
--
Hugo Nebula
"The fact that no-one on the internet wants a piece of this
shows you just how far you've strayed from the pack".