The unit seems to be working now. There has been a couple of mornings where it has failed to fire up with the fan just powering up for a few seconds and then nothing. If I give it a thump from underneath at this point it seems to catch hold and work.
I have a Potterton Prima f60. It tries to start with the fan going for a few seconds and then powers down. I've had someone in but they couldn't spend much time on it due to prior jobs. They tried the PCB but this didn't solve it. He suggested it may be the air pressure switch. I've...