Back in the fall right after I started my combustioneer I was burning leftover coal from my dads house and I shut the stoker down to do some repairs that I hadn't caught before I lit it. I had the power off for about 28 hours, when I dug (with my bare hand of course
) I found some hot fire down in the bottom of the retort
. I also had the power go out for 2 hours with no effects. Then with the last load of coal I had two out fires for no apparent reason.
So I think the coal has a lot to do with how well the fire holds.