MK3S keeps prompting filament change

With the Original Prusa MK3S (and the Original Prusa MK2.5S upgrade), we are introducing a completely reworked extruder with a new filament sensing system. It is a hybrid solution, combining an IR laser sensor triggered by a tiny mechanical lever. This system is not influenced by the optical properties of the filament and is immune to mechanical wear.

What does it look like

This guide is related to the situation when the filament autoload is working (or even if it would trigger only sometimes), yet the printer keeps asking you at the beginning of a print to unload the filament and then to load it back in, in other words, the printer keeps prompting filament change. This means that the filament sensor by itself is working, but not as it should.

In general, the Filament sensor is not vital for the printer, meaning you can always turn it off in the LCD Menu -> Settings -> Fil. sensor (toggle between ON and OFF) and continue using the printer.

Correct connection to the mainboard - It is not uncommon to connect the filament sensor incorrectly.

Troubleshooting

There are multiple reasons why this behavior can appear. Please see IR Filament Sensor Troubleshooting (MK2.5S, MK3S) for how to resolve your issue.

12 comments

EspE2000

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over 1 year ago

I had the same issue. Had about 100kg PLA printed, then after 500 grams of glow in the dark fillament printer started promting me for a fillament change. Printed new part with the metal ball (adapter printer) inside and everything is fine again.

Ricards

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almost 2 years ago

Check the sensor, where the plastic part is moved when the filament is loaded. I had some strings from filament which caused the random filament changes.

KP12

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almost 4 years ago

I went through the test and z live height change with not problems with the filament. Once i try to print from the SD card it will do the check and when it moves to the right hand side, it will stop and tell me to remove filament. Does anyone know why this might happen? and how i may fix this.

David

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almost 4 years ago

Try using one of the pre-slides g-code files which were bundled to the PrusaSlicer. It depends on what printer type you have, but have you been through the [id=112226|title=IR Fliament Sensor Troubleshooting] article?

REEPS

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over 4 years ago

Hi @Prusa ... my IR sensor reads 0 constantly from the beginning ... (never read 1) ... i've checked the connections multiple times, made sure the lever in the extruder is working when i insert filament, checked cables, and nothing ... any ideas? Still can't past first print ...

BoxJockey

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over 4 years ago

Any reccomendations if I am getting this behavior on a MK2S without a filament sensor? Seems to always happen when the print completes,it ejects the filament.

Official Prusa CS

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over 4 years ago

Hi, check your ending gcode, perhaps you're using some kind of multi-material profile.