Same here and depending on pellets. In my P61 the fire brick has had some black what I thought to be soot on it for some time. Today I blasted the stove and most everything in the box was either light grey or grey after that burn. The fire brick still had some soot I thought. It turned out warm today and I shut the stove down and brushed it down when it cooled off. That sooty stuff was just dark ash it came right off with my brush with 0 effort. But this stove has been in a low burn for a couple of days and several days last week too.
Last year I had an ash door gasket that wasn't seating right on my new P61. I changed it out for the next larger size. Someplace around here are photos I posted of that situation and the resulting ash trail that had eye brows of clear area on the door caused I felt by the air leak. We were in a heavy burn time of year though where right now we are doing a lot of low burns out this way. My stove is producing some dark ash, I think darker than during the ash door situation. Many here felt the ash door doesn't play a big roll in flame change when it has a slight leak, not as the main door would, I don't see how that can be.
