could be anything but i would first try the following
switch OFF electrical power to boiler
give the boiler a good whack in top left hand corner
switch power back on
AWOL
July 2012
Is fan working nothing will work if is pack up
ltd
June 2012
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix home heating systems.