I suggest you call a boiler engineer.
Boiler firing is conditional on the correct operation of the fan - a pressure switch detects this and signals the control board.
You have either a fan problem, a case seal problem, a flue problem, a pressure switch problem or a control board problem - and very probably just one of these.
Your engineer should be able to diaganose and repair it quite quickly - be slightly astonished at the cost of spare parts unless the engineer is from British Gas, in which case be very astonished.
Good luck...
Peccavi, April 2009
