What’s the issue?
Snapping can happen at the beginning of the printing or in the middle. It will cause printing stops, printing nothing in mid-print or other issues.
—Old or Cheap Filament
Generally speaking, filaments do last a long time. However, if they are kept in the wrong condition such as in direct sunlight, then they might become brittle. Cheap filaments have lower purity or are made of recycled materials so that they are easier to be snapped. Another issue is the inconsistency of filament diameter.
Re-feed the filament
Once you found that the filament is snapped, you need to heat up the nozzle and remove the filament, so that you can refeed again. You will need to remove the feeding tube as well if the filament snapped inside the tube.
Try another filament
If the snapping happens again, use another filament to check if the snapped filament is too old or bad that should be discarded.
In general, there is a tensioner in the extruder that provides pressure to feed the filament. If the tensioner is too tight, it will cause the filament to snap under the pressure. If the new filament snaps, it is necessary to check the pressure of the tensioner.
Adjust extruder tension
Lose the tensioner a little bit and make sure there is no slippage of the filament while feeding.
Nozzle jammed can lead to the snapped filament, especially old or bad filament which is brittle. In this case, please check if the nozzle is jammed and give it a good clean.
Go to the Nozzle Jammed section for more details on troubleshooting this issue.
Check temperature and flow rate
Check if the nozzle is getting hot and to the correct temperature. Also, check that the flow rate of the filament is 100% and not higher.