hi
i assume it is a condensor boilor, you may have two problems, the control board may be faulty, or i would suspect that the fan is is not working correctly,
you can open the boilor and remove the aluminum cover it has lothes of philips screws in it, then remove the fan and test it with a mains supply lead, minor electrical skills required for this, if you dont have them dont try it.
the fan baldes is attached to a small induction motor it can not be dissasembled so try to free it up with some lubricant while you are testing with mains supply, be sure to unplug it first apply lubracant as many times is necessary.
best of luck, control boards can be bought on e bay cheeper than a main dealer.
best of luck
tom, January 2009
