Heat creep / filament jamming mid-print
Prints fine for a while, then extrusion stops. Pulling the filament shows a swollen, bulbous end above the melt zone.
Needs tuning heat creep jam jamming filament stuck swelling
Likely causes
- Hotend cooling fan failing or weak
- Printing in a hot enclosure
- Too long a retract pulling hot plastic up
- All-metal hotend without a heat break
- Low thermal conductivity hotend
How to fix it
- Verify the hotend heatsink fan spins at full speed and is not blocked.
- Reduce retraction distance so soft filament is not pulled into the cold zone.
- Lower enclosure temperature or add a chamber fan.
- Fit a quality bimetallic heat break.
Work through it in order
The fastest path to a fix
Change one thing at a time and print a small test. Start with the first fix listed — it is the most common cause.