- The filament has probably been a bit overheated (which is what you get with the -too high- default temperatures). The result is a tiny blob at the end of the PTFE tube making it impossible to move the filament either ways.
- Take the head apart : remove the screws holding the PEEK tube (one from above and the other from the underside).
- Cut the filament above the PEEK tube.
- Unscrew the PEEK tube from the heater block : you should see the blob.
- Cut it off, then heat the head and push the filament with a bit or hex wrench. If needed you can clean the nozzle with a guitar string.