The original owners' manual for the Defiant advised keeping the "thumb hole" completely open all the time. I'm glad both of you have solved your problems with the thermostatic control, but I'd be very sure to check your chimneys for creosote build up. With the damper closed, the thermostat closed all the way to start and the thumb hole only partially open, the fire is getting very little oxygen. If the wood is not very dry, the conditions are perfect for creosote formation.
There is another rather exciting thing that can happen. If the wood smolders excessively overnight and oxygen suddenly enters through the loading door or some other place, you can produce ignition strong enough to blow the griddle plate straight up in the air whereupon it will drop into the now raging fire below.
I don't at all mean to be discouraging. The Defiants were/are great stoves. You'll probably not encounter either of these problems, but forewarned is, as they say, forearmed.
There is another rather exciting thing that can happen. If the wood smolders excessively overnight and oxygen suddenly enters through the loading door or some other place, you can produce ignition strong enough to blow the griddle plate straight up in the air whereupon it will drop into the now raging fire below.
I don't at all mean to be discouraging. The Defiants were/are great stoves. You'll probably not encounter either of these problems, but forewarned is, as they say, forearmed.