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Prusa Faults
3 documented Prusa faults, covering MK4, MINI and MK3S. Each entry sets out the symptom as owners report it, the most likely cause, the checks that confirm or rule it out, and whether the repair is worth doing. Everything here is compiled and cross-checked from manufacturer documentation and owner reports — the sources are listed on every page.
Documented faults
- Prusa MK4
Printer stops during Z-axis homing with "Failed to home the extruder in Z-axis, make sure the loadcell is working" and error code #13301
Usually something adding resistance the loadcell reads as the nozzle touching the bed too early — filament drag, a binding trapezoid nut, or overtightened bolts near the sensor — rather than a failed loadcell
Electronics & Firmware 2026-08-29 - Prusa MINI
Printer stops during the initial preheat with "Preheat error print head" and error code #12202, before the print begins
The hotend is not gaining heat at all — usually a broken or intermittent connection in the heater or thermistor wiring at the print head, rather than a failed mainboard
Electronics & Firmware 2026-08-24 - Prusa MK3S
Print aborts partway through with a THERMAL RUNAWAY error, usually right as the part-cooling fan spins up, even though the hotend was heating perfectly moments before
The part-cooling fan is cooling the hotend heater block faster than it can compensate — usually because the silicone sock insulating the heater block is missing, worn out, or the printer's sock/no-sock setting doesn't match reality — which trips the firmware's thermal safety cutoff and looks exactly like a failed thermistor or heater cartridge
Electronics & Firmware 2026-07-11
Categories covered
Electronics & Firmware
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