Boiler was fitted in Feb 06 and have had numerous problems with the CH switching itself off. Baxi have put in 2 pumps, new circuit board and have now installed an Italian fix (a vent on the heat exchanger) as they thought this would solve it. It hasn't and the boiler still switches itself off regularly. Baxi now think its a software fault and are trying to solve it - there is a handful of other cases in UK that are the same - Baxi think it might be unique to bungalows!! Now to top it all the hot water packed up. Baxi came out and found the plate heat exchanger full of black coke like material. They've replaced the heat exchanger and recommended a system clean. The system was cleaned and inhibiter put in before the boiler was fitted. What I don't understand is, how can this stuff be forming on the hot water circuit which is mains fed - surely this should only form on the CH circuit if there was still debris in the system? I've asked our plumber who recogns the boiler my be leaching somewhere but otherwise doesn't know why. He says our boiler is duff and Baxi need to replace or refund. Has anyone any suggestions or answers?