Pretty sure I posted on this last year, but a similar problem has come back


Potterton Prima-F fires up happily on demand, but sometimes, after 5
seconds kills it's gas supply and reignites. This can happen several times,
5 seconds between each occurance. Doesn't always do it.

Last time I was convinced that the thermocouple or control board had an
intermittant fault, but our usual plumber/gas bloke pointed out that the
flame was lifting from the burner, was a bit orange, and that the inner
cylinder of the flue was totally corroded. He was right - Inner annulus was
like a net curtain and leaking exhaust gasses back into the air intake.
Replaced (remarkably expensive for a metal tube) and the problem went away.

Now the problem has come back. This time the burner looks good, bright blue
flame, not lifting, but every few/five seconds cuts out and reignites. It
is sadly intermittant, so whoever I get to look at is likely to waste a lot
of time waiting for the fault.

My guess is the control board (It failed a few years ago and was replaced).

Any other thoughts?

Al.