I had the same problem with my boiler about 6 months ago. I replaced the pcb unit and it works fine now.
Rob
September 2008
it is over heating
John
February 2008
possible overheat or ignition failure. If overheat, check pump. If ignition failure check air pressure switch, spark electrodes or gas valve. If you've no idea what I'm talking about, then call for a fully EXPERIENCED Corgi registered heating engineer