Bad air flow can cause the ash not to get ejected from the burn pot. When was the last time a real heavy duty vent and ash trap clean out was done?
Smokey, that's exactly where we went first with this batch of pellets, last year. I clean the stove about every other day- open it up, vacuum it out top to bottom, empty the ash pan, clean the glass, etc. - the typical daily stuff. Also, because we have a direct vent (good ground clearance) I can take our Shop Vac outside and vacuum out the vent. We have an extra long hose on the Shop Vac. I can feed that hose back through the vent all the way up into the stove from outside of the house. I do that once a week faithfully.
One thing I have for sure found out about our Napoleon- it loves to be clean. Mike from Englander and I did some pounds per hour/BTU/house size calculations online last year, I think, on a cold winter night. The thread's probably still up here somewhere. I let our hopper burn until just about empty on the optimal feed setting. IIRC, it took around 30 hours to burn a 40 lbs. bag? Also IIRC, the Napoleon puts out about 42k BTU on its optimal feed- don't quote me, I'd have to go look it up. The HVAC t-stat in the hallway just outside of the room where the stove is installed was registering in the low 70's? I think? Anyway, we were both commenting on how well the stove was performing- and it does, when we keep it clean. It sure doesn't like to be dirty. In order to get the performance that we know we can get out of this stove, I clean it like a woman possessed.
Anyway, when this batch of Hamers came into the house burning dirty, the first thing I did was clean the stove (again) and vacuum the vent pipe from outside (again) all the way up into the stove. When the Hamers continued to burn dirty, we tore down the stove, cleaned the innards, checked the gaskets (can't remember if we replaced them at that time- I keep gaskets on hand for just such an occasion, so if the gaskets were worn, I'm sure we replaced them.) Hamers continued to burn dirty. We replaced the door gasket, which was admittedly worn. Hamers continued to burn dirty. I called the stove shop, where we bought these Hamers on a bulk buy, and at that time I found out that *everybody* was complaining about this particular shipment of Hamers. It was such a known problem that the stove store replaced all of the bags of Hamers that we'd already burned and with which we'd had problems, and all of the bags of Hamers we had left to burn, and all of the bags of Hamers that we had left on the account. Thank God we'd not picked up the entire bulk buy of Hamers, or we'd be in a mess in terms of space, etc. The store didn't want us to bring back the bags of Hamers we'd already brought home. (We offered to bring them back.)
We decided to try to salvage what we could of those bags of Hamers during the shoulder seasons, when we aren't running the stove 24/7. My husband fabricated a sifter from a large Rubbermaid container that we already owned and some screen. He sifts out the fines and puts the sifted pellets in another Rubbermaid container. These Hamers are still burning a bit dirty but it's a lot better than the unsifted Hamers from this batch: we couldn't burn those at all. They'd clog the burn pot up in a heartbeat. Also, it kind of depends on which bag of Hamers we open. Even sifted, each bag burns differently. Some sifted bags burn fine. Some make enough ash to clog up the burn pot.
This experience was a real surprise for us. We'd burned Hamers quite successfully for two years before this experience. No idea why that batch was so different than previous batches. I wouldn't hesitate to buy Hamers again. Who knows what happened to this batch, and at what point in the process? Even though these Hamers are burning dirtier than any Hamers have ever burned before for us, they are still putting out heat.
In the meantime, and in between, we've burned O'Malley's, Somersets and Presto Logs without incident.
Also, we broke the stove completely down and did a "big clean" before we put her to bed last spring. We started burning the Hamers right out of the gate this fall, trying to get them sifted and used up already- and of course, they came out of the gate burning dirty in a freshly cleaned stove. =/