"Thermal runaway," "heating failed," or MINTEMP/MAXTEMP errors are your printer's smoke alarm. The firmware watched a heater behave abnormally and killed power on purpose. Restarting and hoping is the one move we'll always tell you not to make.
What causes it
- A loose or damaged thermistor — the sensor has shifted out of its pocket or its wiring is failing, so the firmware sees temperatures that don't match reality
- A failing heater cartridge or connector — heat that cuts in and out
- Airflow changes — a missing silicone sock or redirected part-cooling air overwhelming the heater
- Damaged wiring from thousands of toolhead movements
What to do
- Power off. Unplug if you smell anything.
- With the machine cold, inspect the thermistor seating and the harness for visible damage.
- If anything looks off — or the error repeats after one careful check — stop there. This is a $25–60 flat-rate repair for us, and it is not the place for guess-and-check.
Why we're serious: thermal protection exists because unmonitored heaters are the main fire risk in consumer printers. The error means the protection worked. Respect it, fix the cause, and never disable thermal protection in firmware to get past the error.
Still stuck? The diagnosis is free.
Send a photo and a description and we will tell you exactly what is wrong and what it costs to fix — before you spend a dime. We come to you, evenings & weekends, OKC metro. Request a free diagnosis →