Potterton Profle 60e not lighting?

Potterton Profile 60e had developed faulty fan. Changed fan and boiler worked for around 2hours then totally stopped. Let boiler cool down to cold and it restarted. Overtemp had tripped, I reset it but still nothing.

I know if I wait for a couple of hours it'll fire up again. Boiler is getting the "Heat Command" signal from the ecternal wiring but fan isn't even coming on now?

Any ideas?