Prusa i3 MK3S Troubleshooting Wiki

These are a collection of the most common issues for the Prusa i3 MK3S.

A jammed extruder is the most likely reason for filament either under-extruding or not extruding at all.

A partially jammed nozzle can be identified by the filament curling and touching the nozzle as it’s being extruded. The images below show what under-extrusion from a partially clogged nozzle can look like.

There are three solutions (ranked from easiest to hardest):

• Cold pull
• Heat the nozzle and stick a thin needle into it from below
• Depending on where the clog is, manually disassemble and clean the extruder or clean the nozzle

More info here

Clicking noises arise when the stepper motors exert a large amount of force on the filament and must step back to relieve pressure. The filament usually cannot be pushed through because of a jammed hotend.

If a jammed hotend isn’t the issue, take these steps:

• Try increasing the nozzle temperature
• Double-check the alignment of both extruder gears and clean them
• Make sure that your extruder idler is properly tightened
• Verify whether the nozzle is properly assembled into the heater block
  • There should be a space of 0.5mm between the nozzle head and the heater block
• Check for damaged cables

More info here

When printing, sometimes the filament will extrude randomly without sticking to any surface. Loose parts on the printer, such as wires, can brush the extruded filament as the part is being printed ruining the laying process or if the extruder is too high above layers it could cause the filament to not grip the plate/ part properly also interrupting the laying process.

If your filament is stringing, take these steps:

• Check to make sure there are no loose parts hanging such as wires. If there is nothing causing obstruction or interfering with the laying process, move onto the next step.
• Check to make sure that your extruder is not to high above the build platform. Go to Calibration -> First Layer Calibration. During the calibration rotate the knob to adjust the height. View the picture below to see what the filament should look like.

The following sections are adapted from this article and pertain to the Multi Material Upgrade (MMU) specifically. The MMU is a common point of failure on Prusas that have them equipped.

The five LEDs on the MMU correspond to the five PTFE tubes going into the MMU. Each has a green state and a red state.

Selector moved to the current position and ready.

Filament loaded successfully.

The MMU is in the filament loading sequence. Cancel with the middle button.

Wait until the printer finishes the current activity (not necessarily a problem).

Error during filament load. Do the following procedure:

1. Open the MMU and pull the filament out
2. Cut the end at a 45 degree angle and reinsert it
3. Press the middle button to initiate the loading sequence
4. If the LED turns red and green, press the right button for two seconds to resume the print. If the LED turns red, repeat the procedure.

Error during filament unload. Take the following steps:

1. Unscrew and remove the PTFE tube attached to the front of the MMU
2. Pull the filament out of the extruder through the PTFE tube
3. Cut the end of the filament at a 45 degree angle and leave a little bit sticking out of the MMU
4. Push the middle button to reload the filament
5. If the LED turns red and green, reattach the PTFE tube and press the right button to resume the print

Filament is detected in the selector during power-up by the FINDA probe and the MMU cannot execute the standard boot sequence. Usually this means the filament was not properly unloaded last time the printer was powered off.

Simply remove the filament and the printer will continue automatically.

The MMU is not getting enough power. Usually resetting the MMU solves this.

If the problem persists, check all power connections and wires.

If the screen displays “MMU load failed” then that means the MMU properly detected the filament but it didn’t reach the extruder.

Take these steps:

1. Make sure the IR filament sensor is calibrated
2. Check the drive gears and make sure nothing is blocking the filament path
3. Remove the filament and cut the end at a 45 degree angle
4. Reinsert the filament and press the middle button to start the load procedure
5. If the load is successful, press the right button to resume the print

These issues happen infrequently and may only arise a few times over the lifetime of the printer.

Heat creep occurs when components above the heater block get too hot and causes filament to jam. If you have taken the steps laid out under Jammed Extruder and are still experiencing jams, heat creep may be the issue.

To ensure the extruder is being cooled properly, take the following steps:

• Keep a gap of 0.5mm between the heater block and hexagonal head of the nozzle
• Check the extruder fan
• Make sure that the extruder idler screws are properly tightened
• Clean the heatsink of any dust
• Check that the PTFE tube is fully inserted into the hotend
• Add thermal paste to the heatbreak thread that comes in contact with the heatsink
• Lower the bed temperature

More info here

Layer shifting is when the part abruptly shifts on either the X, Y, or Z axis. It is usually either caused by incorrect tension of belts or pulleys not being secure. The first step to troubleshooting this issue is to determine which axis it is occurring on.

Take these steps once you have determined the problematic axis:

• Make sure the extruder and heatbed can move freely
  • The smooth rods should be clean and lubricated
• Ensure the motors and pulleys can move freely
• Check the tension of your belts

More info here

If you couldn’t find your issue here, check out these links:

Official Prusa troubleshooting guides

General 3D printer troubleshooting

MMU LED guide