Hello all, I am running a pellet stove and it starts up great and runs great when it is burning. However, when I shut it off it will go through its normal power down cycle with no problem. Once all the fans and everything shuts down completely it starts leaking smoke into the house. All the vent seals are good. The majority of the smoke is leaking up through the hopper and some is coming out through the ash pan in the bottom of the unit. WHY??? I just vacuumed and cleaned it and that didn't help any. Please help!