Boiler was in the Roe Green, Kingsbury London NW9. I could hear the boiler pump & fan running but after that no ignition..No spark…But E23. Well well Well….. What is the problem..According to the manufaxcture Fan or Air pressure switch..But can you surely tell which one. Even when you can hear the fan running what if the fan pressure is too low to activate the good Air Pressure switch?