Thermal runaway is a safety feature designed to prevent printer accidentally catching on fire in the case of dislodged hotend thermistor. If this feature wouldn't be enabled and thermistor dislodged, electronics would get lower temperature reading and by trying to reach the target temperature, heater would reach dangerous temperatures and printer would potentially become fire hazard.
Thermal runaway is configured to shut down the printer when temperature drops more than 15°C for more than 45 seconds. If the temperature reading doesn't recover in the set time period, printer will shut down and display Thermal Runaway error.
Setting thermal parameters in Marlin firmware
When you get thermal runaway error:
- Check the ambient temperature. Suggested ambient temperature is 20°C or more. Unheated garage in winter might cause thermal runaway as heater doesn't have enough power when the print cooling fan kicks in.
- Visually check the thermistor if it is still securely placed in the heater block body.
- Check the thermistor cable connector on the back of the X-carriage if it isn't loose. This is only an issue with E3D V6.1 with cartridge thermistor. See below.
- Check the fan power settings aren't too high in your slicer of choice and your material temperature. (100% fan is only doable with nozzle temperatures around 200°C with the V6.1 hotend. See below.)
- Check if the fan shroud isn't damaged. In some rare cases users bent it while removing the object or during assembly. This might cause the airflow to be different than originally designed and aiming directly at the heater block. The heater can't be powerful enough to overcome this for safety reasons.