Problem with my W D I3 Plus

Hey, my heater cartridge doesn’t get hot. The display shows nozzle at -15 degrees. After a while I get an error saying “Hardware problem”. I understand that it is, but not what it can be wrong. Any suggestions? Do I need to change the mainboard? Grateful for suggestions.

Broken thermistor or broken wire. -15 means that the mainboard is receiving 0V.

Thanks for the quick feedback. It was the thermistor, poor insulation. I’ve got it working now.