boiler only makes one very short attempt to light then straight to lockout. tried changing PCB as combustion fan running all time, no joy. dissconnected purple connector from gas valve bottom left hand side, now makes 4 or 5 attempts to light before going to lock out. gas valve also now changed , made no difference. what wouldyou suggest.

jim saxton, June 2011

Try the probes in the combustion chamber. They rely on earthing out to convert the voltage from Ac to DC. If its dirty or burnt out it will shut off and go to lockout. Deffo not pcb or gas valve

jeff, July 2011