The fire in your stove CAN get into your hopper under certian circumstances. It has happened to me. I have an Alaska Kast Console II stoker stove. When I run the stove at the lowest setting, say in the early fall or late spring, the coal sometimes doesn't feed fast enough which normally causes the fire to go out. On two occasions though, the fire crept back into the hopper. The reason, which I discovered later, was beause there were coal fines underneath the plate in the coal shute. This allowed air in through the hopper area causing the fire to get into the hopper. After cleaning under the plate the problem was fixed. My stove has a powervent which draws extra air from the stove. Without this, I think the stove would have gone out like it normally does when the coal feed is running to slow.