The technic is nigh the same as for a bowden machine:
- Do NOT cut the filament!
- First heat the hotend to your filament's print temperature or about 20 °C lower
- Then pull at the filament, possibly using a pair of grooved tongues.
If you want to get rid of residue, especially after printing a high-temperature material, you might want to purge the nozzle too.
But the filament is short...
If the filament is too short already, purging it is the solution:
- try to cut the filament to just after the extruder gear
- Heat the hotend to printing temperature of the stuck filament
- insert any other filament that has the same or lower melting temperature behind and (using pliers) make sure that it will line up with the filament path.
- Push the stuck filament through.
- Best perform a purge now.
I mentioned above purging. Purging is just pushing extra filament through. As it melts and gets pushed out with extra force, it takes with it all the residue and old filament. You pretty much purge the old material from the system. It might be easier for you to use a different color, as then you can see when you have purged the previous filament fully.
If you still need to clean more or want to swap the nozzle, you can let the hotend cool down to about 20 °C below the printing temperature of your now-loaded filament and return to a cold pull.
I generally have good enough success by performing a cold pull and then purging some centimeters more after the filament is of even color.
Nozzle geometry warning
Core-Heating nozzles are very complex and doing a cold pull in them is very hard to impossible. It is best to not cold-pull and instead just purge forward if possible.