Thanks Geoff

I had already checked the ignition lead to make sure it wasn't loose

If the fan runs, then it sparks - as it should. However when its not
working, the fan (and indicator light) is off too.

I will test the pressure switch as you suggest. I can sort out the
connections

You supplied me with a fan when the bearings did go! (A year or so
ago) But anyway the fan is not being switched on.

Pete