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Filament bleeding out of nozzle when heating  

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Pepijn
(@pepijn)
Member
Filament bleeding out of nozzle when heating

My prusa MK3S+ 'bleeds' filament when heating up. I replaced the hotend, thermistor and nozzle. I did a factory reset, software update and PID calibration, but the problem persists. When stopping a print, for instance, the filament keeps running out of the nozzle for about 10 seconds. When no extrusion is taking place.

What could be the reason for this ?

Posted : 19/09/2025 12:27 pm
Diem
 Diem
(@diem)
Illustrious Member

How are you drying your filament?

Cheerio,

Posted : 19/09/2025 6:08 pm
Pepijn
(@pepijn)
Member
Topic starter answered:
RE:

Thank you for replying. It is not about the filamet beeing wet. I have more 3D printers and if I try the same filament all is well.

This post was modified 1 hour ago by Pepijn
Posted : 19/09/2025 6:16 pm
Tim
 Tim
(@tim-24)
Member
RE:

For whatever reason my Core One leaves a 2 inch trail of filament dangling after a print, too.  I think its a combination of things to do with how the printer parks the filament: ramming then pulls it out of the nozzle which allows air into the chamber that then heats and forces whatever melt is in the nozzle CHT/HF orifices to feed downward with gravity. A SWAG, and leaves other questions, but it sort of explains why. It does it with several filament types, PLA, PETG, PC-CF, even fresh from the bag Prusament PLA did it. And all leave the same two inch dangle.

 

But wait - you are using a Mk3, sans Nextruder? Then nozzle is too hot or filament is damp. About the only things that will cause it.

This post was modified 59 mins ago 2 times by Tim
Posted : 19/09/2025 6:25 pm
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