Filament and PTFE tube jam
I switched to a different color filament on a newly-assembled MK3 printer, and somehow the filament on the spool became tangled (either when loading or while in storage-it was black so would have been difficult to notice) such that it stopped feeding from the spool mid-print. When I checked on the print, I noticed that the filament was taut and no longer extruding, and the X-axis had been dragged to one side (away from the print). The collision detection did not trigger, so for some amount of time the printer had been attempting to extrude the taut filament.
I immediately canceled the print, cut the filament away from the tangle, and attempted to eject the filament through the menu. However the filament did not budge. I opened the idler door on the extruder to inspect the filament, and noticed that the PTFE tube coming from the hot end (not the short feeding tube in the 3D-printed cap) had been pulled up into the bowden gears, and the end is somewhat chewed up.
Using the amount of force I am comfortable with, the filament does not want to move in either direction with the extruder still assembled, though it looks like the extruder motor shaft may be applying pressure to the filament with the PTFE tube in the way. The tube itself does not seem to want to move.
I would be grateful for any advice on how to proceed. Do any of the experienced printers here know what might be causing the filament to jam the tube so that the tube got pulled into the gears? Is there a way to effectively disengage the extruder motor without completely disconnecting the extruder (I will still need the hotend to function to clear the filament)? Will I be able to replace the PTFE tube in the hotend, or will it still be usable if I can clean up the opening?
I think you need to dis-assemble the extruder and replace the PTFE tube, or at least inspect it and 'repair' if possible.
Loosening the idler tensioner screws will disengage the extruder motors hobbed pulley from the filament, but if the PTFE tube is chewed up, it will probably not help by itself.