How does Prusa3D firmware respond to an open or shorted thermistor during a print? I have a Prusa3D i3m3s.  The problem occurred once before with firmware 3.6.1.  Last night I upgraded to firmware 3.7.1 and repeated the problem almost exactly.

The symptom is that at what appears to be the same point in the print in the two failure instances, the extruder stops extruding.  There are a few wisps of filament on both failures.  The print continues to completing.  At the end of the print, the firmware issues an error because the MMU2s can not properly retract the filament.

On analysis, the filament is tightly jammed into the extruder and hot end, almost as if there has been heat creep.  Slow, strong, and steady tension on the filament will withdraw it from the extruder system.

The hot end heats normally, and maintains temperature.  When hot, plastic extrudes properly from the hot nozzle.

The thermister wires are damaged from an earlier problem.

The damage points to a thermister-related problem, but a shorted or open thermister is easy to detect in firmware.  I would expect it to throw an error and stop the print.  

My question is:  Does the Prusa3D firmware detect open/shorted thermisters and stop the print?

If a photo is required, I can post that tomorrow.
This sounds like a problem I had with my hotend cooling fan a couple years back. To answer your question, from what I'm reading, the Prusa3D firmware detects thermal runaway if the hotend temperature drops for more than 45 seconds, it detects an open-circuit by reading 16&nbsp;&deg;C or less (MINTEMP error), and detects a short by reading 310&nbsp;&deg;C or higher (MAXTEMP error). 

Couple questions that might help better troubleshoot the root of the problem:


have you measured the thermistor's resistance while cold or hot?
have you made sure your hotend cooling fan is at an appropriate speed while heated?
have you made sure your print cooling fan duct isn't pointed at the hotend block due to being jostled?


You might find that there are some fairly simple solutions to a handful of overheat problems. I bought a cheap knockoff all-metal heatbreak and immediately ran into problems, but solved them by printing a better heatsink shroud and upgrading to a 40&nbsp;mm fan. If you've upgraded to an all-metal hotend, you might run into issues with PLA specifically if you're not printing enough material fast enough, as PLA is somewhat sensitive to heat creep through the filament itself in the throat of the hotend.