potterton Performer 24 is faulty?

My potterton boiler will not fire up the red light comes on stating no flame, have replaced the Pcb card with new, all the limit switches seem to be working the over temp switch is ok the heat sencer appears to be ok (Have a resistance reading across it I think it could be a thermister type sencer)
the flue extract fan does not come on (no supply to it) it also seems that there is no supply to gas valve solenoid, no ignition
the pump motor runs and you can hear the relays on the PCB card pullin.can you point me in the right direction as to what to look for, the boiler is a potterton performer 24.
Many thanks

bernard Douglas
February 2008