I have an Enviro Empress that lights and burns fine. After about 30-45 minutes the fire starts to die out. The auger drops pellets, but not enough to keep the fire burning. Doesn't seem to be a clog in the auger because it runs fine to keep the fire on high for the first half hour. I have cleaned the front of the firepit, behind the front panels, and the exhaust pipe. Please help, and thank you for your time.