short bypassing variable resistor?

hey! So i have an SMTmax concentrated hot air gun.

The problem i am having with it, is the heat in which the air comes out is always at 500 Degrees. you can not cange the temperature at all

There is a variable resistor that controls the heat as a knob on int interface. my first thought was that there is a short in the resistor itself, but after opening it up, a quick test with the multimeter showed that its resistance was reading as desired.

After this, i pulled the resistor off completely, and the heat was still at max. I'm pretty sure breaking that circuit SHOULD stop the circuit from working, but I am not certain of it. this makes me feel like there is a short somewhere bypassing the resistor itself.

I've reballed everyjoint, and there is no board damage. now i am at a loss as to how exactly to find the failing component. if anyone has experience with these circtuits, please let me know. i would really appreciat your help.