We have cleaned our NPS 45 inside and out, installed a new igniter and also replaced the door gasket. The stove is 6 years old but has always run great. Lately we have noticed that the burn pot continues to get filled with pellets after several hours and they seem to choke off the air flow from the burn pot. Napoleon gives instructions on how to slow the rate down and we have tried this but it does not seem to help. Any ideas?