Half way through printing a series of pieces for a Cosplay prop, I was
greeted by this:
I tried restarting the print for the model I was using, and it automatically stopped with the same error twice more, each time about 5 minutes into the print.
The Prusa Support site has a section on thermal runaway, and various forums seem full of questions about Thermal Runaway, with relatively few useful answers. In my case, running PID Calibration (from the Info Screen go to Calibration and then PID Calibration) fixed the problem.
PID Calibration is a nearly automatic process – the printer will prompt to to set the hotend temperature to 210°, after which it will raise and lower the temp through five cycles, as it tries to tune it’s PID Controller.