Yes the damper changes the burn alot,If i open it much it will start the burning pellets jumping around in the pot and clear open it can get them popping out of the pot I dont open it more than about 1/4 way on heat 3When was the last time you cleaned the vent pipe? Does the damper have any affect on the burn?
Maybe the triac on the board is overheating and is going out of its normal stat.