Problem: Temperature reading def

Today I stumbled upon a quite annoying problem and was wondering if anyone here has experience with it and can help me solve it. I'm running rep 0.91 on a davinci 1.0 and in the middle of a job it stopped printing and the temperature readings said def (short for defect I assume). I tried printing again and this time it barely started when the same thing happened and when I checked the temperature logs it seems that the extruder had a very high pitch temperature before it started to cool down. When I noticed it a minute later both the extruder and heated bed temperature value was: def

My guess is that it's related to the thermistor.