sorry but you are wrong , the problem is lack of air in the combustion chamber, the boiler is asking for air just like you need oxygen to live the boiler needs air to work satisfactory
terry
September 2013
most likely the heat exchanger is scaling up. will need cleaning or replacing. but i would also check to see if the diverter valve is not at fault. a good idea would be to put some cleaning agent like sludge remover into the rads for a few days first and drain the system, then fix the heat exchanger, then add inhibitor to the system.
kash
September 2013
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.