First, STOP!
Make certain black knob is not slipping! If you see knob is snug then read on.
Thermostats are calibrated on a machine in our factory and cannot be adjusted in your home.
The tension needed to turn the dial is adjustable when done correctly.
1) You'll need vise grips, flat blade screwdriver, sharpie, 5/32 or 7/32 t-handle allen wrench.
Step by step.
Unplug fans from wall. Remove entire fan assembly from thermostat side of stove.
Using a Robertsons #2 square drive, remove cover from thermostat. DO NOT REMOVE SILVER SCREW LOCATED HIGHER UP ON COVER. You may need to use wood dowel or handle from hammer to push up on edge of cover. This can take some real effort depending upon how snug it is. To be clear, only the two black #2 screws hold it. Remove cover.
You we see a set collar on the 1/4" rod running from thermostat knob to thermostat.
Use a Sharpie and make a reference mark on the rod to the black set screw. This is critical to avoid messing up calibration!
Next, clamp the vise grips onto the rod 1/8" from set collar. Next, place flat blade screwdriver in gap between collar and vise grips. Next loosen set screw BEING CAREFUL not to allow it to rotate away from sharpie reference mark.
Twist handle of screwdriver, which will push set collar towards thermostat thusly increasing pressure on the washer on inside of set collar.
Tighten set screw firmly. Remove vise grips, verify alignment of set screw to sharpie reference mark. Turn knob...you should feel increased tension. TURN THERMOSTAT TO LOW, reinstall cover.
Typing on this phone isn't easy!