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Clogged nozzle: material stops coming out

Severity: HighAffects: Filament (FDM)Updated July 27, 2026

Symptom

The extruder turns or makes its characteristic click but no material comes out, or very little and irregularly. Prusa describes a partial clog as the case where the printer pushes some material but not enough, with gaps and incomplete layers, and with the filament curling up instead of coming out straight.

Likely causes

In order: the most frequent cause comes first.

  1. 01Carbonised residue from a previous material inside the nozzle
  2. 02Mixing materials with incompatible temperatures, for example loading PLA after polycarbonate without purging
  3. 03Heat creep: heatsink cooling fails, heat travels up and the filament softens inside the tube
  4. 04Dust or particles carried in by the filament
  5. 05The nozzle too close to the bed on the first layer, blocking material from escaping

How to fix it

Apply one fix at a time and reprint the same test part. Changing three settings at once tells you nothing about which one worked.

  1. 01

    Do a cold pull

    Medium

    Heat the hotend to printing temperature, load filament, let it drop to the pull temperature your maker specifies and pull firmly in one motion. A plug shaped like the hotend's interior comes out, bringing the residue with it. Repeat until the plug comes out clean.

  2. 02

    Check the heatsink fan

    Easy

    If the clog always happens partway through a print rather than at the start, suspect heat creep: Prusa explains that when the heatbreak gets too hot, heat travels upward and the filament softens inside the hotend. Check that the heatsink fan spins freely and is not blocked by dust or a stray piece of plastic.

  3. 03

    Clean with a brass needle, never a steel one

    Easy

    With the hotend hot, insert the correct-diameter cleaning needle through the tip and push the residue through. Use the needle supplied with the printer: a drill bit or steel wire can score the orifice and ruin the nozzle permanently.

  4. 04

    Replace the nozzle

    Medium

    A nozzle costs little and saves hours of attempts. If two cold pulls have not cleared it, swap it, and take the chance to fit hardened steel if you print fibre-filled materials. Always tighten hot and with the right spanner so you do not damage the heater block.

How to prevent it

  • —Purge thoroughly when changing material, especially when stepping down in temperature
  • —Keep the heatsink fan free of dust and filament debris
  • —Use dry, clean filament and consider a sponge filter at the inlet
  • —With abrasive materials, hardened steel nozzle from the start

Sources

  1. [1]Clogged nozzle (CORE One, CORE One L, XL, MK4/S, MK3.9/S) | Prusa Knowledge BasePrusa Research · Manufacturer · accessed July 27, 2026
  2. [2]Extrusion stopped mid-print (Heat creep) | Prusa Knowledge BasePrusa Research · Manufacturer · accessed July 27, 2026

Related problems

MediumFDM

Stringing: threads and cobwebs between parts

Fine plastic strands are left between two parts of the model, or between two objects on the same plate. Prusa calls it 'hairy prints'. In severe cases the part is covered in a web you have to remove with a knife or heat gun.

HighFDM

Under-extrusion: less material comes out than it should

Material lines are missing within layers: gaps appear between beads, walls look thin and translucent, and the part breaks easily. Prusa describes it as layers missing material and fragile parts that tend to fall apart.