9 times out of 10 the problem is with the seals in the telescopic flue. The burner will light and the boiler will run for a while, the problem is that the oxygen in the combustion chamber is burnt and the carbon monoxide which is passed out of the flue is sucked bak past the seal into the combustion chamber. No oxygen=no ignition.
The other fault when the boilers buzz first thing in the morning is the ignition system. this runs when the boiler starts its pre ignition sequence and will run on for a while once the boiler has ignited. The locout on the initial start up is lack of oil in the majority of cases and can be cured by inserting a non return valve in the line approx 1 mtr fron the boiler
Mark W
September 2010