please help! Baxi 105e keeps cutting out after about 30mins. It will reset only to cut out again. Red lights flash indicating flame failure and air flow. Plumber has been several times and checked flue and fan and can find no problem he has also changed the air pressure switch but this still hasn't cured the problem. He completely stripped down the boiler but could find no obvious problem. He is still trying to rectify the problem but in the mean time i'm left with no heating or hot water most of the time and it's driving me potty. Please help!