THERMAL RUNAWAY
Prusa 3D Printer
Severity: CriticalWhat Does This Error Mean?
Thermal Runaway on a Prusa printer means the temperature is not being maintained as expected. The thermistor may be loose, the heater may be failing, or there are drafts cooling the hotend. Check thermistor placement and run PID calibration.
Affected Models
- Prusa MK4
- Prusa MK3S+
- Prusa Mini+
- Prusa XL
Common Causes
- Thermistor not seated properly in the hotend
- Heater cartridge loose in the heater block
- Draft from window, AC, or fan cooling the hotend
- PID values incorrect after hotend modification
- Printer in a very cold room (garage, basement)
How to Fix It
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Check the thermistor — make sure it is seated in the hotend.
The thermistor must be fully inserted into its hole in the heater block. The retaining screw should hold it firmly.
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Tighten the heater cartridge screw.
A loose heater cartridge causes uneven heating and temperature drops.
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Run PID calibration from the printer menu.
LCD Menu > Settings > Temperature > PID Calibration. This optimises the heating algorithm for your specific setup.
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Use an enclosure in cold environments.
Printing in a cold room or near drafts can cause temperature fluctuations. An enclosure keeps ambient temperature stable.
Frequently Asked Questions
Is Prusa's thermal runaway protection better than Creality's?
Prusa has always had thermal runaway protection enabled by default. Older Creality printers sometimes shipped with it disabled. Both are critical safety features.
Can PID calibration fix thermal runaway?
Yes, if the cause is poor temperature control rather than a hardware fault. PID calibration tunes the heating algorithm to minimise temperature swings.