I have a 3 year old baxi boiler that has developed a problem. When the water or heating is switched on after about 10 or so seconds the fan or flue warning light comes on.After resetting a dozen or so times i can get the heating running but if you run a hot tap then sometimes water gets hot sometimes the boiler switches to fan or flue warning and shuts off. I had the flue and fan checked and was told they were ok but still get the same problem. Just wondered if anyone else has come across this problem or if its a costly fix or is there anything i could replace to save a fortune on a plumber, thanks