I asked my browser about pellet smoker burn back on shutdown and found a lot of comments about the same problems with Traeger, Pitt Boss and others. And the causes and corrections to prevent were all similar. There are several articles that explain the cause and suggest the best cure. Nothing new found there. One prominent cause was thought to be damp or previously wet pellets or poor grade pellets and pellet dust. As a result some suggest only using enough pellets for the cook and removing the left over pellets after the cook.  Not my problem here, as the climate is drier, my grill is stored on a covered porch, and is covered with a good cover. Most common suggestion in a hot cook is to lower temp setting to the 200-250* range and then shutdown; which is what we are doing, and successfully. Also avoid ash buildup in the fire pot. Clean it out before hot cooks or after long low/slow cooks.

Also of note is that on a hot cook, opening and closing lid frequently or for prolonged time causes the temp to go down and the PID to dump more pellets and then if you turn off then, there is a big bonfire in progress in your fire pot and with the auger not moving, it is easy for this fire to ignite auger pellets in the adjacent tube. The fan then "fans" the fire in the tube during the shutdown. Makes sense to me.  So I came away with the following suggestion. 
If you make a hot cook; after you remove the cook, allow the pit to stabilize at the high temp for enough time to burn the extra pellets. ( i.e. 10 or so minutes? the time will help burn up drippings also)
Then turn down to the 200-250* and shut off at that temp. That is what I did with the test yesterday.  Worked for me.

I will not comment on how to treat a hopper fire as I don't have that experience. I do have a fire extinguisher that will put out grease fires and does not harm the smoker. Perhaps others will advise on this. 
 

 

MAK advises to leave the lid open during shutdown. I’ve gone from grill mode (500-600°) to immediate shutdown mode with no burn back issues following that advice.

MAK advises to leave the lid open during shutdown. I’ve gone from grill mode (500-600°) to immediate shutdown mode with no burn back issues following that advice.

 That works well for burnback prone pits.  The smoldering fire @ shutdown seeking oxygen can burn its way out by not drawing air thru the auger/hopper as there is plenty of more easily  accessed air with the

 lid open.  This shutdown method goes back to the early days.  BTW: The lid doesn't have to be wide open to function if inclement weather is a concern. Propped open ~ 1" works.

I can see where opening the lid might might help the fire pot burn out faster. But if you open the lid before pushing the off button, you will get loading of the fire pot to compensate for the lost temp and "that" plus then stopping the auger will leave you with the bonfire I mentioned above. I really believe that is the biggest contributor to auger ignition. Scenario, has been: Open lid, check steak/chop and if done remove steak/chop, then hit the off button. Or, if not done to close and open again in a few minutes, then remove steak/chop and hit "off".  Bonfire, fan on, and auger off = auger pellet ignition IMO.(that is why the auger fire and/or hopper smoke mostly occurs during shutdown). If you are going to try that, I would be sure and keep the lid closed for a while after removing your cook, then when temp is stable again, shut it off.  Personally, I am happy to reduce the set temp first and then the off button, as this allows the fire pot to burn down, as the auger slows delivery, and allows you to turn off with minimal stimulus for bonfire. On the RT's I am not sure whether the pellet dump at the end of shutdown, would hinder or help this quick shutdown process. "Shutting down my smoker is like a box of chocolates: You never know what you are going to get."

Long term follow up on 1070 mod and shutdown adjustments.
1. Sealing hopper lid--no episodes of smoke from hopper either during cook or shutdown. Problem assume solved.
2. Leaving high temp setting after cook removed until PID equilibrates to the set temp and then lowering temp to 225-250 range before shutoff. --No episodes of auger smolder or burn, except the one time I did not leave high temp stabilize before lowering temp. Problem assumed solved.
 

4 months later. 1070 well used, and no burn backs since last note. Grill very reliable, and I would recommend it.

Glad it's working well for you.   

Glad it's working well for you.   

Thanks!

Since my DC went txx,s up (headed to grave yard) and my Traeger has been marginal, I'll give it a look.

Since my DC went txx,s up (headed to grave yard) and my Traeger has been marginal, I'll give it a look.

Let me know if I can help or with any questions.