When the fan runs it makes a circuit through the air pressure switch and then ignition commences, no ignition with the fan running points to the APS. If the APS is closed circuit and it has no voltage through it then the control pcb may be faulty, if the APS is open circuit with the fan running, and has voltage waiting , then the APS is faulty. This is assuming the fan is in good condition and running at normal speed.
Jonny, November 2011
