I've been having issues with thermal runaways lately due to random temperature spikes on my Ender 3.

I figured it was out of calibration so I did a PID tune and still had issues. I then replaced the thermistor and I'm still having issues. I'm going to try replacing the heater element tonight.

However, if anyone has some suggestions, please let me know.

Plot of temperature spikes

  • $\begingroup$ The image doesn't seem to support the thermal runaway issues, a runaway is not recoverable as the printer shuts down (if firmware is properly configured). Could you please give some more information? E.g. when does it happen; randomly, when the part cooler fan kicks in, when the head is a certain position over the plate, etc. $\endgroup$
    – 0scar
    Apr 22, 2021 at 6:23
  • $\begingroup$ When I had similar issues, the crimp on the thermistor connector on the board was loose $\endgroup$
    – towe
    Apr 22, 2021 at 13:37
  • $\begingroup$ The thermal runaway protection was activated when it would spike above 250C. The problem was the heater element. As I was removing it I found a bend in the wire that seemed to have been the bad connection point. My temps are stable now. At least this go around I installed quick connectors so I don't have to redo the wire loom every time I replace the heater or thermistor $\endgroup$ Apr 25, 2021 at 17:18

1 Answer 1


It looks like a sensor issue. Maybe a temporary resistance in a contact of the sensor circuit made the temperature look low to the controler, so it applies power to raise the temperature. When the contection recovers, the temperature is too high, so the controller lowers the power to restore the temperature.


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