We just started using our VF100 in our new house. It was professionally cleaned a few weeks ago and we used it for about a week before vacuuming out the stove and ash pan with a shop vac/filter. There were some unburned pellets. We cleaned it on Saturday and by Monday night the ash pan was filled with unburned pellets. I vacuumed it this morning and ran it all day, and again it's full! We are using Northern Warmth Supreme Douglas Fir, they were left in the house by the old owner. The picture shows after 12 hours of use today. Any ideas of what could be wrong? Thank you!