Earlier this season, I completely cleaned my pellet stove from the chimney down. When I fired it off, the thermometer showed 400 degrees at 5%, which was great. Over a period of about 2 months, the temperature has slowly dropped and dropped. Today it is reading just 290 which is a drop of over 110 degrees. Does it need cleaned again or could it be it's colder now or could it be the pellets? Just curious.