It was advised to me, the key to avoiding burn backs are to be on top of basic maint better (admittedly the one I had was likely my fault). I'd been lax about keeping the level of ash in the fire pot down. I am usually pretty good about getting my little shop vac in there at least every 2nd to 4th cook (depending on lengths of previous cooks). And when it happened I'd let a HUGE pile of ash build up. (had slipped my mind due to so many other things going on). I knew it was due but forgot how "due" it was
I also had just finished a high heat steak cook. At about 475 deg. And I put the grill directly into shutdown from high heat and went inside to finish prepping and then to have the meal.
Oddly the grill's (I guess most of them) shutdown mode is not by temp but by time. So, I put it in shutdown, the ash pile was up to the level of the auger, thanks to my 475 temp cook when the fan cut off there were plenty of very hot ashes that just could not wait to have a party in the auger. Was only when I went back outside to pull it into the garage I noted smell of smoke and almost ignored it. But, I opened the grill lid. Nothing, but opened the hopper and smoke coming from the hopper.
So, I drained the hopper (thankfully the fire had not reached the bottom of the pellet pile). Once drained I did a restart on the grill, and put it into prime mode, to force out as many as I could. Next AM I vacuumed out everything. Been fine since.
Since then I never do a shutdown directly from high heat on either grill. My thinking is on any given time IDK what had been happening in the pot. So, my shut down process is to step. Turn the grill down to a lower heat or "smoke" setting. Let it run that way, then once it's stabilized shut it down. I guess it wastes some pellets but rather that then a burn back