The boiler has just been serviced and lots of new parts fitted, On firing up all works fine for approx 15 seconds then the flame cuts out but the motor keeps running, after approx 10 seconds the flame fires up again for 15 seconds and the same thing happens. If I remove the front door/cover of the boiler it all works fine as it should until I refit the door/cover then the same thing happens. It is as if the burner is not getting enough air/oxygen. The boiler has a balanced flue which I have checked and there is no blockage. Do any of you clever chaps have an idea of what could be causing this and where I should be looking.