Thermal runaway

Updated 2 weeks ago ​by Tomáš Chvalina

The Thermal runaway error occurs when the temperature readout of the hotend drops by 15°C for more than 45 seconds or heatbed for more than 4 minutes while printing. It is a safety feature which prevents the heater from reaching dangerously high temperatures if the thermistor become loosened.

Make sure to distinguish between the Thermal runaway error and the Bed thermal runaway error. 

  • Thermal runaway - indicates a with the temperature readout of the hotend
  • Bed thermal runaway - indicates a with the temperature readout of the heatbed

Troubleshooting

Thermal runaway

  1. Check the ambient temperature. Suggested ambient temperature is 20°C or more. An unheated garage in winter might cause a thermal runaway error if the heater doesn't have enough power when the print cooling fan kicks in.
  2. Keep the printer away from any unintentional sources of cooling. Positioning the printer near an air-conditioning unit or opened window might be the cause of unwanted temperature drops. 
  3. Visually check the thermistor to see if it is still securely attached in the heater block body. 
    1. The thermistor's connector can become loose over time, so first of all, try reseating it. If it doesn't help, it usually means that the small thermistor wires have broken off inside the connector. Your best bet is to cut away the connectors completely, connect the wires directly and solder them together. 
  4. Make sure the fan power settings aren't set too high in your slicer of choice. Also, check the material temperature settings. (100% fan speed is only possible with nozzle temperatures around 200°C with the V6.1 hotend.)
  5. Confirm the fan shroud is not damaged. In some rare cases, users bend it while removing the printed object or during assembly. This might cause the airflow to be different than originally designed and it can cause the fan to blow directly towards the heater block. For safety reasons, the heater isn't powerful enough to overcome this.
  6. Try to initiate PID tuning

Bed thermal runaway

  1. Check the ambient temperature. Suggested ambient temperature is 16°C or higher. An unheated garage in winter might cause a bed thermal runaway error if the heater doesn't have enough power when the print cooling fan kicks in.
  2. Keep the printer away from any unintentional sources of cooling. Positioning the printer near an air-conditioning unit or opened window might be the cause of unwanted temperature drops. 
  3. Make sure the bed thermistor is still secured underneath the golden Kapton tape.
  4. If you are printing small objects with PETG, try to print more of them at once or place them away from the center of the heatbed. 

Do not hesitate to contact us at info@prusa3d.com if you would have any further questions.
 


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