You say you had a full bed of coal. And then discovered it wasn't coal, it was all ash in the shape of coal. That tells me you way over fired the stove. You're lucky to have a home to come home to. The good part is; you know your chimney is safe. Now I'll tell you how it happened; At tending time the fire was low. You tended the stove as always, then left for work. Because the fire was low, the new batch of coal somewhat smothered the fire you had, and would be a while before it catches. ( Fred, you'll appreciate what I'm about to say next). Meanwhile, the FAN continues to pull heat off the mass of the stove body, causing the back flapper to open more, and more, as the stove cools more, and more, as the fan continues to pull the heat off. The flapper door opens wide enough that it shifts just right, and hangs up. It doesn't always happen, but it does. And it did in your case. Now, the fire finally catches, and roars away, as if the ash pan door was left open. Your stove got soooo hot, the extreme heat threw your spring out of calibration. It either broke the spring, popped it out of a notch, or something. What ever happened to the spring, was enough to let the flapper drop back closed. Or was it still open? Those bimetallic thermostats are quite simple. Take it apart, and you should be able to see how it goes back together. Moral of the story is: If you're going to tend your Hitzer, then leave before seeing the "Dancing Ladies", TURN OFF THE FAN. So the house may be a little cooler to come home to. At least you'll have one too come home to. I too have a good safe chimney. Oliver EDIT: Your spring needs to set up under the cover more clockwise. Lets say 9:00 position(cold). 7:00 position(hot). Looks like you're at 5:00.
Last edited by oliver power
on Thu Jan 23, 2014 7:37 am, edited 3 times in total.