He should have wrote down the draft tests,in your manual,for future repairs.Also,setting it with the damper is not going to help your problem(I think) he should have gotten into the hidden settings,also.Did the new burn pot fit better?or is the stove built wrong?(it does happen).But,just back to what we said,before,your pellet flue(the pipe) ends inside a huge pipe,then goes to the roof,this is not acceptable by the enviro manual,and is part of your draft problem.Some stoves can handle the extra pressure,of a big pipe conversion like that,some cannot.The cold air,dropping into the big pipe,knocks down the ability of the little motor to force it up.