There are several reasons why filament may not come out of the nozzle:
Clogged nozzle: A clogged nozzle can prevent filament from flowing through. This can happen due to material debris, contamination, or incompletely used filament.
Incorrect settings: Incorrect settings such as an extrusion rate that is too low or a nozzle temperature that is too low can cause filament to not come out of the nozzle.
Blocked extruder gear: If the extruder gear is blocked, it cannot grip the filament properly and it will not be pushed through the nozzle.
No Tension: If the filament is not properly tensioned, it may twist and not flow through the nozzle.
Defective nozzle: A damaged or defective nozzle can prevent filament from flowing through.
Defective Control: A fault in the printer's control system may prevent filament from coming out of the nozzle.
To correct the problem, you should first clean the nozzle, check the settings, and make sure the filament is properly tensioned. If the problem persists, it is recommended that you check the extruder and replace it if necessary or contact a professional.