This has been loosely discussed in the coal burning thread, and I figured it was time for it's own thread.

My Heatmor has been boiling over recently. This occurred first as I had 80 lbs of anthracite burning in the OWB. I figured that 80 lbs of coal was too much to cool down once the blower kicked off, and that just pushed the water temps too high. I let the coal burn off and loaded up with just wood and it did the same thing as soon as I turned my back on it. I attributed it to the 3 straight days of 35-50 MPH winds "sucking" the blower's close off flap open via natural draft.
Well, it boiled over on me again tonight after 2 days of running fine. Perfectly calm day, full load of wood, high 30's outside. The high temperature safety shutoff had already killed all power to the unit. I went inside and filled up the boiler really quickly (took a good amount of water!!) and then filled the water bladder up halfway like it's supposed to be. The blower was off and the firebox door had been closed for at least 10 minutes before I opened it up. I had a ROARING fire in the fire box. I closed the firebox door and threw a board over the chimney. About 10 seconds later I had a bunch of smoke coming out of the blower. I took the blower unit off very carefully and I caught the problem red handed. The flapper door had gotten enough creosote built up on the hinge that it stuck open. I had kind of cleaned it up about 4 days ago when I first suspected that door to be an issue, but I didn't really clean it hard. A little bump and the flapper closed on it's own.
So, I cleaned the whole hinge area up with a wire brush tonight making sure it was all shiny metal before I put it back into the unit. Thus, I've found my problem.
Now, a solution??
How do I make it so the door is forced shut when the blower is off? Attached are a couple of pictures of the construction of the unit and how it goes into the boiler.


