Folks, mine was installed about 7 years ago. I have used different pellets over the years and this is the first time it has happened. It doesnt happen often but usually happens right after cleaning the pot. I clean the pot almost every day (no more than two days) to remove build up and provide a better burn. I do use a thermostat and have for the last 5 years without problems.
My, when on high, is dropping (unbelievably) burning pellets from burn pot into ash pan. It doesnt always happen. I removed the ash pan to watch the fire from below and check the pot clean-out plate to make sure it is closed and no gap. It is unbelievable to me that pellets are escaping through the small holes in the pot or around the igniter but I see no other way it can happen.
With that said, this year I am using American Biomass Clean Fire Premium Wood Pellets - ash < 1.0% and fines < .5%. These pellets are definitely burning hotter and slower than others since I had to slow the feed rate down almost all the way. But it seems the pellets sizes vary quite a bit. Is it possible that they are simply floating around with the blower and actually able to "escape" the pot?