Clogged nozzle: identifying the causes and clearing it

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A clogged nozzle is one of the most common problems in 3D printing, and usually no reason to panic. In most cases it can be cleared again with simple means. With printers that have a quick-change hotend, replacing it is also done in a few minutes if in doubt.

Safety first: The hotend gets hotter than 200 °C. Work with gloves or tongs, do not touch the heater block and follow your manufacturer’s instructions. For many printers, taking the hotend apart is described in the maintenance guide.

How can you tell a nozzle is clogged?

• When loading filament, nothing at all or only a thin, curled thread comes out of the nozzle
• The extruder clicks or rattles because the gear slips
• The print suddenly shows severe gaps or fails
• The filament shows ground-away spots where the gear has slipped

A partial clog often looks like under-extrusion.

Typical causes

• Heat creeping upwards: If the filament softens above the nozzle, it sticks there. This often happens with PLA in enclosed, warm printers.
• Too much retraction: Soft material is pulled back into cold areas and solidifies there.
• Dirt or foreign bodies: Dust on the filament, burnt residue or particles from filled filaments.
• Changing material without purging: If a residue is left in the nozzle after a high-temperature material such as PETG or ABS and printing continues with PLA at a low temperature, it can harden.
• Temperature too low for the material.

Clearing the nozzle, from simple to involved

1. Push through hot

Heat the nozzle to the material’s printing temperature; going slightly above usually does no harm. Push filament in by hand. Often a small plug comes loose this way.

2. Cold pull

A proven method for pulling residue out of the nozzle:

1. Heat the nozzle to printing temperature and push some filament through.
2. Lower the temperature significantly, to about 90 to 110 °C for PLA. The filament becomes tough but not hard.
3. Pull the filament out with a firm, steady pull.
4. An impression of the inside of the nozzle with the contaminants should be hanging on the tip.
5. Repeat until the tip looks clean.

Special cleaning filament is also suitable for cold pulls. Exactly how the cold pull works on your printer is often described in the manufacturer’s maintenance guide.

3. Cleaning needle

Many printers come with a thin needle. With the nozzle hot, carefully insert it from below to loosen residue. Do not use force, and only use a needle that is thinner than the nozzle opening.

4. Replace the nozzle

If none of this helps, replacing it is often the quickest solution. Nozzles are wear parts. On many current printers the complete hotend or the nozzle can be changed without tools.

How to avoid clogs

• With PLA in enclosed printers, open the door or lid so that heat does not build up
• Do not overdo retraction, guide values are in the article Stringing
• When changing material, purge thoroughly, ideally at the higher temperature of the two materials
• Store filament clean and dry
• For abrasive filaments with carbon or glass fibres, use a hardened nozzle