There could be one or more of many problems.
If your boiler has a perminant piolt (ie is lit even when boiler is not running) and this has gone out then your boiler will not come on and problem could be caused by a faulty thermocoupler.
If it has an electronic piolt (ie only lit when call for demand) you could be looking at:-
Fan running but too slow to operate air pressure switch (faulty fan)
Faulty air pressure switch itself.
Faulty PCB, not sequncing the lighting procedure
Faulty gas valve (PCB sequncing but valve not operating)
You need to call a Corgi Engineer as these are not jobs to be tackled by anyone unqualified.
You can find Corgi engineers by using the postcode search @ www.trustcorgi.com
Robin S
August 2008