Filament Jam
Twice now I've gotten filament jams that were very difficult to clear. Once was my fault when I had programmed a filament swap, but left the room. When I finally remembered, the printer had safely shut down and the filament had cooled into the shape shown in the picture. The second time, it was on a print with a high number of retractions. The filament finally just quit extruding and I ended up with the same type of jam.
Both were cleared by pulling VERY hard on the filament (probably not the best idea), but no amount of nozzle heating and attempts to extract the filament seemed to work. I have two questions:
1. Why is this happening?
2. What is the best way to clear this if it happens again.
I'm running a kit built MK3S with the latest firmware.
RE: Filament Jam
The drawing shows the Prusa modified heat break; the base bore diameter is 2.2 mm until it reaches mid-neck, where it contracts to 2.0 mm, the same diameter as the nozzle bore. Filament pulled from the hot end will generally show the 2.0 mm diameter section. In some cases it will show the 2.2 mm diameter section. When you see 2.2 mm, then a step down to 2.0 mm, it indicates a possible blockage source. Your filament looks normal, something else is probably happening to prevent filament extrusion.
Check the filament drive gear if firmly attached to the motor shaft. The idler tension is correct (adequate). That there is not undue resistance turning the filament spool or feeding filament.