I have a Hudson River Westpoint stove that has a slotted bottom on the burnpot. I seem to have an issue with a buildup of material in the burnpot that is too heavy to go into the ashpan and builds up in the burnpot and restricts airflow. Have been using the same brand of pellets from the same batch, so I don't think they are the issue The buildup can get as much as an inch or so thick after a bag of pellets, but doesn't happen all the time. Any ideas?