Filament plug at start of every print

Hi! I’ve been printing on minis for 5 months now, and I love them! I’m up to 3 minis now, but my third one is presenting with a puzzling issue.

At the start of every print, I have to remove the filament and snip off the final half inch or so of filament. It looks like the filament is not being retracted enough, and is left in a hot section of the hot end to pool, until it forms what I would say is a 3.5 or 4mm plug that will not move through the hot end at all. After I snip this slightly thicker tip off the filament, the printer runs perfectly. If I don’t remember to snip the end of the filament, the plunger is unable to force the filament through the hot end. In fact, when at melting temps I cannot even force the filament through with my hand.

My other two minis have never had this problem. What could be causing this third mini to create filament plugs after every print that have to be snipped off? What can I do to fix it? I’m reasonably familiar with the individual components of the hot end assembly and carriage, and I’m not at all averse to taking it apart.

Sounds like heat creep… check to see if your heatsink fan is working. Surprised this doesn’t affect the printer while printing.

Both fans are working perfectly. I assume if it was heatcreep, there would be negative effects during the print? Everything prints flawlessly when I snip the end of the filament before allowing the print to start.

Attached is a picture of what is left in the nozzle after a print is left to cool. Upon closer inspection, I discovered that he filament past the white, slightly less wide portion is actually hollow.

Yeah, if it were heat creep, I would expect it to affect your prints. Try the filament in one of the other known good printers.

Already done. Its not just PLA, its also ABS. Any filament I use does this, and only on this printer. My other two are fine.

New guy here, just started with 3D printing and have yet to have to clean my hot end so I have no idea how much work this would be. But since you got one machine that does not work and two that do the traditional machined shop diagnostic procedure would be to start swapping parts.
I imagine the nozzle would be easy, not sure about the hot end, if there are connectors it should not be that bad but if it is hard wired all the way back to the control board it would be a pain.