Time to get yourself a copy of the manual.
Is it a two-piece fireback or one piece?.
Very key to good operation is proper size chimney flue. These need a 8" flue pipe, trying to reduce it to 6" or connecting it to inadequate chimney is asking for problems. Preferably an interior chimney with two stories of height exiting near the ridge pole. These need good draft to run right assuming the internals are not plugged.
The key to the Defiant is a hidden chamber behind the fireback. It must be cleaned with a vacuum cleaner yearly with thin vacuum brush through a hidden access plate in the top of the stove accessed through the flue pipe opening. Its a cast iron plate under the internal damper. Fine ash will fill in the hidden chamber preventing the primitive second stage combustion system from working. Just as important, lack of flue gas flow behind the fireback creates a temperature differential between the front of the fireback and the rear of it, causing the fireback to warp and crack. The two piece firebacks are less prone to this but it still can happen but less expensive to repair.
The last issue is "backpuffing". The Defiant is a very high output stove designed to heat large spaces like a poorly insulated "barn" of a house. They throw off lots of heat. When they are used in a smaller better insulated space they really do not like to run at low output and they do not like to idle. Standard practice is for people to run them during the evening, then load them up with wood and crank the damper down. The problem is the stove has a hot bed of coals and will convert the fresh wood to gases but the air damper will be near closed preventing oxygen from fully burning the wood. The hot unburnt gases will fill up the chimney until they find a source of oxygen from the top of the chimney and they will ignite causing a small explosion in the stack and the stove. The net result is puff or huff from the stove with the thermostatic air damper snapping open and closed. It can and will lift the top cooking plate. Many Defiant owners leave a cast iron water pot on top of the cooking plate to weigh it down.
The solution to back puffing, is if you need to slow down the amount of heat, you need to do it slowly reducing the amount of wood as the evening goes on and avoid loading it up before going to bed unless you leave the air damper alone or slightly increase its opening. It will create a burst of heat but which many do not want, but if the air damper is closed down to reduce the heat with a fresh load of wood, the stove will backpuff on occasion. It may not happen all the time, in many cases, windy conditions cause turbulence in the stack and that seems to make it worse.
BTW, Defiants can be creosote makers if run in primary air mode with green wood. They are also not much more efficient than a box stove if run in primary mode. Ideally get it started in primary mode, then once up to temperature, flip the damper down and run in secondary mode.
