Generic boiler ignition sequence goes something like this : power on -> pump runs -> flow switch operates -> fan runs -> air pressure switch operates -> boiler goes to ignition. If fan is running but but boiler does not go to ignition, then I would start with the air pressure switch. You would need a fully EXPERIENCED Corgi registered engineer to test this component. It could well be the PCB which is causing this problem, but it is most likely to be the A.P.S. Hope this of some help.
Curtis Lee Patrick
February 2008
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