My BAXI System 35 boiler went on the blink today.
It has been running well for 3 years now.

The fault lights suggest 'fault with fan/flue'.
I have checked the fan is turning fine, and have checked that the
micro-switch on the flu pressure sensor is operating correctly. I
have also traced the wiring back from the microswitch on the pressure
sensor to the PCB and that seems OK to.

My guess is that it must be the PCB which is faulty.

The symptoms are...
After resetting the boiler and setting the CH Demand on, the boiler
pump and fan run up, and after about 10 seconds the flu/fan fault
light starts flashing. The pump and fan continue to run.

Should I go ahead and replace the PCB or could it be something else?