continued; "starve/smother" a term i made up myself to describe what happens when fuel feed is interrupted long enough to cause the fire to drop to coals then feed resumes and the fire relights as the stove cools until it either warms back up or hits the low limit and shuts off. things that can cause this are usually associated with high draft air and low fuel feed (burning fuel faster than it is fed) however in a clean stove this usually doesn't result in much more than a dirty burn from constant relighting (think about how an igniter stove smolders to ignition, now imagine it doing that every several minutes) not a danger thing if dealt with in a reasonable time frame. now in a dirty stove this can cause a later more delayed re-ignition after the fuel has piled up much farther thus creating the "fuse" i referred to earlier.(remember when the fire dies the stove starts to cool and an ashed up heat exchanger will cool faster as ash insulates the remaining heat from the low limit switch, stove shuts off as its relighting and here we go with a smoldering fire under a connected fuel pathway. stoves equipped with vacuum interrupt switches for the feed system (usually designed to stop feed if either the draft motor stops or if the door or ash pan is unsealed) if they aren't able to be kept "satisfied" they will drop feed as well, here's the technical part of dropping vacuum due to resistance. temperature and air density are inversely proportional, hot air is lighter and therefore does not produce as much vacuum pressure at the same velocity as cold air does, so a restriction in the air pathway or in the vacuum port will allow feed at cooler temps but not at hotter ones, so the stove will feed until it drops vacuum, cool off then feed again. if the timing is right you can get a starve smother restart which can happen after the low limit is reached resulting in the same scenario. i could go on but it would get too boring for most to suffer through i suspect in closing folks, i didn't write this to scare people away from pellet stoves, i myself have for years gotten up in the morning and left for work with my family sleeping in their beds and my pellet stoves purring along. if that's not a ringing endorsement for these machines i cant do any better. a properly maintained pellet stove be it mine, or anyone else's made today (or within the last few decades like these old whits the OP has, are designed to prevent this issue from happening, unfortunately there is no foolproof method to "build" a burnback proof stove some may say there are some out there , i personally don't believe it with all due respect to the manufacturers of these units. the designers of Titanic said she was unsinkable as well. anything can happen under the right circumstances. BUT, the technology employed in these devices make it a rare occurrence and in most cases (not all, i wont say that) there is a maintenance issue involved. NOTE i am not blaming our OP for his incident i believe he has done his due diligence in that he has worked on trying to get this unit (a used one which he had no control over until recently) properly serviced to the best of his knowledge going in, we don't blame here we educate! bottom line folks, a well maintained pellet stove can be among the safest heating appliances available, even in a failure such as this , the fire cannot get out of a fastened steel box, smoke may get out which sucks, but with good smoke and CO detectors (i don't care what you heat with , GET THEM! maintain them test them and replace them when the manufacturer's posted lifespan is up) damage and injury can easily be averted. but folks we gotta maintain these units, read your manual contact your dealer or manufacturer if you are unsure of anything. inspect your gaskets regularly and replace them if suspect even if its before the manufacturers suggested replacement cycle hasn't been reached yet. dont forget the chimney! its just as important as the stove is. its as simple as this; a clean well maintained stove will be there for you when you need it, neglect your stove, and she'll let you down when you need her the most.