When the boiler gets a "call" for heat the fan runs.
A pressure switch detects that the fan is running OK and the control board opens the pilot gas valve and makes sparks to light the pilot flame.
You should hear the fan running - if it isn't it's probably broken - if it is running there is possibly a problem with the pressure switch or maybe just maybe the control board.
A decent boiler engineer should have you up and running in an hour or so - unless it's a guy from British Gas who will insist on installing a completely new boiler and then not offer any guarantee unless you pay more to have the radiators flushed out!
Good luck...
Peccavi, March 2009
