Hotend thermal runaway #26204 (MK4S) #13204 (MK4) #21204 (MK3.9)

This article is also available in following languages: 

What happened?

The printer is showing the error "Hotend thermal runaway: Check the print head thermistor wiring for potential damage".

Error name: Hotend thermal runaway 

Error code: #26204 (MK4S) #13204 (MK4) #21204 (MK3.9)

The error will show if the temperature on the nozzle drops by 12 ºC for an extended period of time. This temperature drop would usually not be an issue, but if the heat is not recovered after 60 seconds the error will happen. In this case, the printer will stop the heating and display the message on the screen.

How to fix it? 

Make sure that the ambient temperature where the printer is is stable, and above 10 ºC.

Extruder inspection

This error can be caused by any damage to the hotend heater or the hotend thermistor.

Make sure that the hotend thermistor is inserted in the heater block.

Access the LoveBoard. Check if the heater and the thermistor are connected correctly and if there is no damage along their length.

If you have a multimeter, you can use our Multimeter usage guide to check if the cables are damaged.

xBuddy board inspection

On the MK4/MK3.9 main board, check if the fuse that protects the hotend is not damaged.

Make sure that the Loveboard main cable is correctly connected to the xBuddy board.