Yep, it's the controller that determines the percentage performance of the pellet stove.
P is the distance from the actual temperature to the desired temperature, I is an addition over time, and D is an opposite force, D should not be used for a pellet stove, so it should just remain 0.
Without having graphs to look at it is difficult to adjust the controller and I recommend P 2 and I 0.2 D 0
You can watch many videos about PID controllers on Youtube.
