Prusa 3D Printer Error Code 6: How to Fix It

Medium 15-60 minutes Medium Severity Verified June 2026
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Error Code
6
Brand
Prusa
Product Type
3d_printer
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
15-60 minutes
Prusa Error Code 6 indicates that your printer has encountered a condition requiring an M999 reset command — a firmware-level instruction that clears a halted or stopped state and attempts to resume normal printer operation. This error typically appears after a print failure, thermal runaway event, or an unexpected firmware stop that left the printer in a locked state. In most cases, this is a recoverable situation and does not indicate permanent hardware damage, but it should be addressed carefully before resuming any print jobs.
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Tools You'll Need

How to Fix Error Code 6

  1. Power Cycle the Printer

    Do not simply unplug the USB cable from the host computer — you must use the printer's power switch or disconnect the main power supply to perform a proper power cycle.

  2. Send the M999 Command via Host Software

    Do not attempt to resume a print immediately after sending M999 without first verifying that the print bed, nozzle, and all axes are in a safe home position.

  3. Identify and Resolve the Root Cause

    If you see signs of scorching, melted wiring, or the printer stopped due to a thermal runaway event, do NOT restart the printer until the root cause is fully inspected and repaired.

  4. Update or Re-flash the Printer Firmware

    Only download firmware from the official Prusa Research website (prusa3d.com). Using third-party firmware files can void your warranty and introduce new issues.

  5. Inspect Thermistor and Heater Wiring

    Always unplug the printer from the wall outlet before inspecting or touching any internal wiring. Allow the hotend to cool to room temperature (below 40°C) before handling the extruder area.

  6. Check the PINDA/SuperPINDA Probe and Endstops

  7. Perform a Full Factory Reset as a Last Resort

    A hard factory reset will erase all saved print profiles, PID tuning values, and calibration data stored on the printer. Make a note of any custom settings before proceeding.

Parts You May Need

Hotend thermistor
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Heater cartridge
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PINDA or SuperPINDA probe
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Hotend wiring loom / cable bundle
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Hotend thermistor
Check Price on Amazon
Heater cartridge
Check Price on Amazon
PINDA or SuperPINDA probe
Check Price on Amazon
Hotend wiring loom / cable bundle
Check Price on Amazon
Hotend thermistor
Check Price on Amazon
Heater cartridge
Check Price on Amazon
PINDA or SuperPINDA probe
Check Price on Amazon
Hotend wiring loom / cable bundle
Check Price on Amazon
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When to Call a Professional

Contact Prusa Research support (help.prusa3d.com) or a qualified electronics technician if Error Code 6 recurs repeatedly after completing all steps above, if you find visibly burned or melted wiring near the hotend or mainboard, if the mainboard itself shows signs of damage (burn marks, failed MOSFETs), or if a thermal runaway event caused physical damage to the heat block or heater cartridge. Prusa offers direct support and warranty repair services, so reach out to them before attempting mainboard-level repairs yourself.

Frequently Asked Questions

What does Error Code 6 mean on a Prusa 3D printer?
Error Code 6 on a Prusa printer means the firmware has issued or requires an M999 reset. This typically happens after a critical event — such as a thermal runaway, a firmware-triggered STOP command, or an unexpected halt — that locks the printer from operating until it is explicitly cleared and reset.
How do I send the M999 command to my Prusa printer?
Connect your Prusa printer to a computer via USB and open PrusaSlicer (go to the Console tab in the printer control panel), Pronterface, or OctoPrint. In the terminal/console input box, type M999 and press Enter or click Send. The printer should respond by clearing the halted state and returning to idle.
Can Error Code 6 damage my Prusa printer?
Error Code 6 itself is a safety mechanism — it is designed to halt the printer to prevent further damage. However, if it was triggered by a thermal runaway event, there may already be underlying damage to the thermistor, heater cartridge, or wiring. Always investigate the root cause before resuming printing.
Why does Prusa Error Code 6 keep coming back?
Recurring Error Code 6 usually points to an unresolved underlying issue such as a failing thermistor, a faulty heater cartridge, corrupted EEPROM data, or damaged wiring causing intermittent faults. Try updating your firmware, inspecting all hotend wiring, and performing a factory hard reset to resolve persistent cases.
Is it safe to keep printing after sending M999 to clear Error Code 6?
Only resume printing after you have identified and resolved the root cause of the halt. If the printer stopped due to a minor glitch and all hardware checks out fine, it is generally safe to continue. However, if the halt was caused by a thermal runaway or hardware fault, printing without fixing the underlying issue is unsafe and could cause fire risk or further printer damage.

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