Boilers of this age typical follow the following sequence:-
They will do nothing if the over heat has been tripped. This is a button that when pressed goes in with a click. If it does not require reseting it will be floppy. The electronics in the PCB then check that the air pressure switch is open. The fan is then powered. The electronis check the air pressure switch is closed. The semi-permiant pilot is then lit. Flame retification is used to verify the pilot is lit. The main burner is then lit.
I suspect that your problem may be the fan has stopped working. You will need to get a Gas Safe engineer to check to see if there is voltage on the fan. If there is the fan could be freed with WD40 or oil. This would prove if the fan is the only thing at fault but the fan should be replaced as once they have been stationary the coil will be damaged and it is likely to fail subsequently.
Peter, November 2009
