Biomass Boiler Question?

[UpsyDaisy]

We have had our biomass (exterior) boiler for 4 years now. After an initial set of teething problems, this has run well until last week. Last week we heard large 'popping' sounds then plumes of smoke out of the flue and boiler itself. When the guy came to sort it he found it had blocked with pellets deep inside the boiler. He had never seen this before, anyway fixed it Monday and it was fine until last night when it did the exact same thing. So he came this morning and 'reckoned' it was to do with 'atmospheric pressure'. Does this make sense, because if it does and bearing in mind it didn't happen through all of the storms last year, or since installation, what do we do? It now means I have to turn it off each time I go out!!!!!! I am terrified if its on I could smoke out the neighbours.