Does your Boiler have a Square Flue Terminal or a Round one?
please reply to this as it does make a diffrence
I think your experience just shows what OFTEC OFT 101 actually teaches somebody with NO EXPERIENCE, what is happening to your boilr whilst not common, is not that unusual, and I am supprised that an engineer who regularly works on oil fired appliances, has not come accross this problem before, if charged £1-00 for each time i found this kind of fault I would now be a very rich boy!!