Can anyone help? our boiler "glow worm economy plus 50F" has just started playing up. The pilot light is lit, the ignitor keeps sparking, but the main burner doesn't light every time. I have removed the front covers to gain access to the burner & heat exchanger & given it a good vacuum out just in case it was some dirt somewhere. Coild it be something to do with the pressure inside the unit, as sometimes for some strange reason I could get the burner to light with the front covers off, but as soon as the covers were back on, it wouldn't light. I have also had it where the burner won't light without the covers on, indicating that there must be some sort of pressure sensing system.