Well folks, I had a suspicion I had a problem - ever since I got my new BK Princess Ultra (freestanding) last autumn, and it looks like I was right. I finally removed the cover on the thermostat. I tried to do it awhile back, and after I removed the two square-drive screws, it was still really stuck in the back (up against the stove) and I was afraid to beat on it too hard, given the dire warnings against removing said cover (on the sticker). But the tech guy at BK said it was fine to remove it, once he realized I wasn't an idiot. And with the stove hot, it came off quite easily. Removing the cover does not affect the airflow, although of course you want to replace it when done trouble-shooting. One thing he said (IMPORTANT): turn the control knob down so that the flapper is close to fully-closed before re-installing the cover, lest the edge of the butterfly flapper wedge against the cover. So here is what I found. I set the thermostat control at about 2 and left it there throughout this experiment. I measured the width of the valve opening - between edge of flapper and the opening (where is unimportant, as long as you're consistent). With the stove almost completely cold, it was about 1-1/8" open. I built a good fire and after an hour or so the opening was close to 2". I let the fire burn down overnight and by morning the stove was pretty cold and the opening was down to 1" or so. Clearly this is wrong - for a given control knob setting, the valve should close as the stove heats up and open as it cools down. I confirmed this with BK and the dealer is sending me a new thermostat assembly with prepaid return label for the old one. It appears to be held in place by two screws and some silicon sealant (presumably some high temperature variety, hopefully available locally). So stay tuned ... The kicker is ... even with this gross malfunction, this is still, by far, the best woodstove I've ever had, easily keeping a fire going for 12 hours !