Well British Gas have finally come up trumps. I resisted the offer of a powerflush and a new engineer was sent. He agreed with a previous diagnosis of flow and return to the boiler being plumbed in the wrong way round. He drained the system, re-plumbed it in about an hour, fired it up and it's been working nicely all day. Amazingly the system had worked for 5 years being plumbed wrongly, but at least we've got a warm house now. Thanks to Peter from BG.

Thanks, I just checked the pump setting and it is on 3, so back to drawing board. Pump outer casing was very hot to the touch so I guess it's working pretty hard even when boiler trips out.

Well, I'm finding out more than I wanted to know about powerflush. We've had 5 Brit Gas visits on the Homecare contract. They changed the pump and all the stats on the Potterton 100 boiler which keeps tripping out on overheat. Yesterday they recommended powerflush and magnaclean for £848. Although, still not a guaranteed fix. Claim I wouldn't pay if it didn't work. I would be prepared to get a powerflush although not at BG prices but as we can get all the rads hot before the boiler trips I don't see how it can be a circulation/debris problem. Any ideas anybody.