I have an older free standing harman accentra chain driven pellet stove, bought off market place. When I bought it the fine box was full of fines clean out and it worked for a while then started making weird thumping noise and stopped working, in the fine box was full size pellets no fines. Had it professionally cleaned he though it was just cheap pellets after one day of burning with good pellets it was making the same thumping noise when auger was turning and now the finebox has full size pellets again and stove quit working. Why am I getting full size pellets in my finebox?