Hello weactivist,
Best way to check the thermistors, is to do it powered off and in cold condition (room temperature). Because the THERM1 and THERM2 are NTC resistors.
Put your multimeter on 200 kΩ and measure the leads of the NTC (or terminal THERM1 and THERM2). You should measure something between 70 to 100 KΩ depending how hot the NTC is. If your measurement is way lower than, it’s possible that the NTC is shorting out. Detach it, check it and attach it again.
Check also if the NTC is centered in the heater block. If outside the heater block, or half in & half outside, You’ll get wrong temperature readings “measuring” back. Check also the wires of NTC (fault contacts).
Best regards,
Velleman Support