In message , Steve
writes
On Sat, 17 Sep 2005 19:34:40 +0100, Steve wrote:

One slightly disturbing thing I noticed when listening carefully this
afternoon was that after the fan starts up and before the ignition
attempts, there is a electric buzzing/crackling sound, as if electricity
is arcing somewhere.

A correction: the buzzing/crackling sound occurs immediately before the
*fan* starts, not before the ignition attempts.

Then apart from what I said before, could be the air pressure switch or
a relay on the pcb

--
geoff