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Fix

Clogged nozzle

Something blocks the nozzle or hotend so filament can only trickle out or stops completely, starving the print or ending it early.

Likely causes
  1. Heat creep from poor hotend cooling
  2. Debris or burnt residue in the nozzle
  3. Nozzle too close to the bed on the first layer
  4. Leftover higher-temperature material
  5. Excessive retraction
  6. Gap between nozzle and PTFE tube
Clogged nozzle
Extrusion that thins out, curls sideways or stops entirely, often with a clicking extruder and a print that ends in air with missing layers.

What a clog is and how to confirm it

A clog is any blockage in the hotend that keeps filament from flowing freely. A partial clog causes under-extrusion and inconsistent lines; a full clog stops extrusion. Prints often fail midway with the upper section missing while the nozzle kept moving through the air.

Confirm it by heating the nozzle to the normal temperature for the loaded material and extruding 20 to 50 mm through the printer menu. A healthy nozzle produces a steady, straight strand. A partial clog gives a thin strand that curls to one side; a full clog gives nothing while the extruder clicks or grinds. If you can push the filament by hand only with heavy force, the blockage is in the melt zone or heat break.

Causes, most likely first

  1. Heat creep. The heat sink fan is weak or blocked, so filament softens above the melt zone and swells.
  2. Debris or carbonized plastic from dust, cheap filament or long idle heating.
  3. First layer too close to the bed, which backs up pressure.
  4. Old material left behind, for example ABS or PETG residue when printing PLA at a lower temperature.
  5. Too much retraction pulling molten plastic into the cold zone.
  6. Gap at the PTFE tube in lined hotends where plastic pools and hardens.

Fixes, cheapest and fastest first

1. Raise the temperature and push

Heat 10 to 20 °C above normal printing temperature and push filament by hand. Often this clears soft residue.

2. Do a cold pull

Heat to printing temperature, push filament through, then let the nozzle cool to about 90 °C for PLA (or around 140 °C for nylon cleaning filament) and pull the filament out firmly. The tip should carry a dark plug of debris. Repeat until it comes out clean.

3. Clear from below

Use an acupuncture needle or the cleaning needle sized for your nozzle, pushing up from below while hot. Do not ream hard; you can widen or scratch the bore.

4. Check hotend cooling

The heat sink fan should run at full speed whenever the hotend is above about 50 °C. Clean dust from fins and replace a weak fan. Reduce retraction to the normal range: about 0.5 to 2 mm on direct drive, 4 to 7 mm on Bowden.

5. Reseat the PTFE tube

On lined hotends, heat, then cool, cut the tube end square and push it firmly against the nozzle so no gap remains.

6. Replace the nozzle

If the blockage will not clear, replace it. Tighten new nozzles hot, at around 240 to 280 °C depending on the manufacturer, while holding the heater block, to avoid leaks.

Material notes

  • PLA: the most prone to heat creep because it softens at low temperatures. Avoid long pauses with a hot nozzle.
  • PETG: sticks to nozzle walls; purge well when switching.
  • ABS: prints hot and can leave residue that later blocks PLA. Purge with the new material at the higher temperature first.
  • TPU: buckles rather than clogs, but excessive retraction and fast speeds cause jams.

Prevention checklist

  • Keep the hotend fan and heat sink clean.
  • Do not leave the nozzle hot and idle for long periods.
  • Purge thoroughly when changing materials.
  • Use filament dust filters and store spools covered.
  • Keep retraction within normal ranges.
  • Use hardened nozzles for abrasive filaments.

Frequently asked questions

How often should I replace a nozzle?

There is no fixed interval. A brass nozzle used with plain PLA can last a long time. With abrasive filaments such as carbon fiber, glow-in-the-dark or wood fill, brass wears quickly, sometimes within a few hundred grams. Replace the nozzle when it clogs repeatedly, when line widths grow, or when the opening looks worn or misshapen.

Is it safe to use a needle on a hot nozzle?

Yes, with care. Use a thin needle sized for the nozzle bore, hold it with pliers or a holder, keep fingers away from the heater block and push gently upward. The goal is to dislodge a particle, not to scrape the bore. If gentle pushing does not help, do a cold pull or replace the nozzle instead.

Why does my printer clog only on long prints?

Clogs late in long prints are often heat creep. Over hours, heat travels up into the cold side if the hotend fan is weak, the heat sink is dusty or the enclosure is too warm. Filament softens too early, swells and jams. Clean the heat sink, confirm the fan runs at full speed and, for PLA, open or remove enclosure doors.

Other print problems

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