The door of our woodstove is held on by two set screws, but one of them has been missing for years -- probably since we moved in, though I'm not totally sure of that, because I didn't notice it until we'd been in the house for a while and I investigated the fact that the handle was feeling loose.
Probably because the door wasn't sealing perfectly tightly as a result of this screw being missing, the door has gotten slightly warped. It doesn't get as tight a seal on the top as it should, so the wood burns hotter and faster than it ought. But the degradation was gradual, and we didn't really realize for a while, let alone figure out why.
When we did we called the company we bought it from, and they sent someone out who fixed things up pretty well. He adjusted everything, and replaced the set screw, so the door's seal is now much better (and the improvement in how good it burns is marked) though still not perfect. So they're ordering a replacement door. Best part, this is all on warranty. We love Hearthstone Stoves.