"John Stumbles" wrote in message
...
Phillip Brown wrote:
Just to update the thread, I tested the fan on separate mains and it ran
fine. Turned out the air pressure switch was stuck, which the Potterton
troubleshooting flow chart pointed me to. Cleaning it out resulted in a
working heater.

Are you saying that because the air pressure switch wasn't working the fan
wasn't coming on? That's puzzling me because AIUI on these boilers the fan
runs whenever mains is applied regardless of the air pressure switch, but
the latter has to operate to make the boiler light.

The fan was off when the air pressure switch was stuck in the wrong
position. I removed the fan from the boiler and tested it separately and it
ran fine. I replaced it, and as soon as the pressure switch was cleaned and
went back to the correct position, the fan started and the boiler ignited.
That's all I can tell you