i had a similar problem on my combi boiler and it turned out to be that when it was fitted the flue was getting rain water down it which then blocked up the air pipe starving the boiler and therefore it went into lockout ( the gas needs to burn with oxygen). The flues are usually a double skin/wall type... one part is to to let out the burnt gas and the other to supply oxygen/air for the bolier to burn with the gas. Try checking inside the boiler for water or another type of blockage... I have known things like wasps nests for example in flues which will block the air supply...but in my case it was water in the pipe which i sorted out by fixing the felt in my roof ... sod's law that when the boiler was fitted the flue was right in a spot through the felt that water ran down! it also only used to block after heavy rain which need i say is what we've been getting lately... hope this may be of help
russ, July 2007
