Sometimes, the Bowden tube will pop out of the extruder. It can happen at either end, but I have found that it happens much more frequently at the extruder end.
This can be caused by two things:
- Clog in the nozzle. The nozzle gets clogged, then the extruder keeps pushing filament. Eventually, the Bowden tube will pop out to relieve the pressure.
- The teeth in the pneumatic coupling have worn out. In my experience, this comes from frequently removing the coupling and pushing it back on. If this is the case, you just need to get a new coupling.