Symptom: nothing comes out of the nozzle, or you get a thin, ragged trickle instead of an even cylinder of plastic. The extruder is working, the motor is humming, and the material is not moving. With a partial clog the print carries on, only the walls get thinner and thinner and the top layers start to look like a sieve.
A clogged nozzle is any restriction in the plastic's path between the drive and the outlet hole. It is not always a physical piece of dirt in the hole itself. Far more often the plug forms higher up, in the transition zone between the heatsink and the heater block, where the plastic softens although it should not yet. Telling a full clog from a partial one matters in practice: a full one stops the print immediately, while a partial one can ruin prints for weeks before anyone looks inside the hotend.
Most common causes and fixes
1. Heat creep, or heat crawling up the hotend
The heated zone ends where the cooled heatsink begins. When hotend cooling is inadequate, that boundary moves upwards. The filament softens while still in the tube, swells, fills the entire bore and sets into a plug the moment the print stops or slows down. The characteristic symptom: the first half hour or so is flawless, then extrusion weakens, and once the printer has cooled the filament can be pulled out together with a thicker, deformed tip.
How to check: confirm that the hotend fan spins throughout the whole print, not just once temperature is reached. A jammed fan, a dusty heatsink and an overly warm enclosure around the hotend all produce the same effect.
What to do: clean the heatsink, replace the hotend fan with a working one and make sure nothing is blocking the airflow. If you print in a closed chamber at 50 °C for ABS or ASA, feed the hotend fan cooler air from outside the chamber. Also check that the nozzle is not sitting at temperature needlessly through long pauses.
2. An abrasive material has eaten a brass nozzle
Filaments with a carbon fibre additive wear brass away within a few dozen hours of work. The hole first widens and loses its roundness, and its edge becomes uneven. Matted fibre catches on that edge and builds up a deposit, right up to a full clog. Porima rates the abrasiveness of PLA/CF and ABS/CF as very high, and with these materials a hardened nozzle is required, not merely recommended. PA and PLA Wood fall into the medium category and will also shorten the life of brass.
How to check: unscrew the nozzle hot and inspect the hole under a magnifier. A rounded, enlarged edge means the nozzle needs replacing, regardless of whether it can still be cleared.
What to do: use a hardened, steel or carbide nozzle for fibre-filled materials. Also keep the recommended diameter in mind: PLA Wood and PLA Star are printed with a 0.6 mm nozzle, because the filler does not pass freely through 0.4 mm. For PLA/CF and ABS/CF the manufacturer itself gives a minimum feature size of 0.4 mm, while the remaining materials go down to 0.2 mm.
| Porima material | Abrasiveness | Recommended nozzle | Diameter per manufacturer |
|---|---|---|---|
| PLA/CF | very high | hardened required | 0.4 mm |
| ABS/CF | very high | hardened required | 0.4 mm |
| PA (nylon) | medium | hardened recommended | 0.4 mm |
| PLA Wood | medium | hardened recommended | 0.6 mm |
| PLA Star (Sparkle) | none | brass is sufficient | 0.6 mm |
| PLA, PETG, ABS, ASA, TPU | none | brass is sufficient | 0.4 mm |
Source: the official FDM technical data table from the manufacturer, Porima. Temperature ranges for all materials: 3D printing temperature table.
3. Changing material without purging the hotend
A residue of PETG in a hotend heated to 210 °C for PLA will never melt; it will simply char and break away in pieces. It works the same way in the other direction: PLA left in a block heated to 280 °C for ABS carbonises and forms hard crumbs that block the hole at the least expected moment. The difference between the bottom of the PLA range and the top of the HT PETG range is almost a hundred degrees.
What to do: when moving to a cooler material, first push through fifteen centimetres or so at the previous material's temperature, and only then cool the hotend to the new temperature. When moving to a hotter one, heat up to the new temperature and purge the hotend until the flow is a single colour with no streaks. For large temperature jumps, do a cold pull.
4. Dust and contamination drawn in with the filament
A spool that has stood on an open shelf for a month collects dust along its entire length. The material carries it straight into the nozzle, where the particles sinter into a deposit. The same mechanism applies to crumbs left after the drive gear has ground the filament, and to metal particles from a worn knurl.
What to do: fit a simple filter to the filament, for example a piece of sponge in a clip, just before the entry to the extruder. Store spools in airtight containers with a desiccant, which incidentally solves the problem in point five as well. Regularly vacuum plastic shavings out of the inside of the extruder.
5. Wet filament
Water turned into steam increases the volume of material in the channel and throws the flow out unevenly. The result is intermittent extrusion, and along with it charred residue on the channel walls. Damp nylon can block a nozzle within a single print. Porima rates PA's moisture resistance as low and treats drying as mandatory: 8–12 h at 65–80 °C.
How to check: extrude material into the air with the printer stationary. Crackling, steam and a trickle bending sideways instead of falling vertically are an unambiguous sign of moisture.
What to do: dry the spool. HT PETG, ABS, ASA and PC/ABS need 6–12 h at 40–60 °C, the PLA and PETG family usually 2–4 h at 30–40 °C, and PLA/CF 4 h at 55 °C. The only material that does not need drying is HIPS, because it is not hygroscopic. You will find the details in our filament drying guide.
6. A gap between the PTFE tube and the nozzle
In hotends with a PTFE tube run all the way down to the nozzle, the tube must press against its seat without the slightest play. If even a tenth of a millimetre of gap is left after a nozzle change, molten plastic forces its way into that gap, sets, and forms a ring that chokes the flow. The symptom is a clog that comes back a few days after every clearing.
How to check: heat the hotend, take it apart and inspect the face of the PTFE tube. A blackened, conically flared end confirms it.
What to do: cut the tube square with a sharp knife or a dedicated cutter, and on assembly tighten the nozzle hot so that the tube is pressed down from above. A PTFE tube is not suitable for prolonged work at the temperatures of technical materials, so with ABS, ASA, PA or HT PETG consider a hotend with an all-metal break.
Quick checklist
- Check that the hotend fan is running and the heatsink is clear.
- Do several cold pulls in a row and inspect the plug you pull out.
- Clear the hole only when hot, and only with a needle thinner than the hole.
- Inspect the nozzle hole under a magnifier and replace it if the edge is rounded.
- Fit a hardened nozzle for PLA/CF and ABS/CF.
- Dry the filament and fit a dust filter ahead of the extruder.
- Check that the PTFE tube is pressed against the nozzle seat.
The overriding rule: change one parameter at a time. After every correction run the same flow test, so you know what helped.
How to do a cold pull
The method works better than poking with a needle, because it removes deposit from the whole channel rather than just the hole. Heat the hotend to the normal printing temperature of the material in question and push fifteen centimetres or so of filament through by hand. Then lower the temperature gradually and watch for the moment when the plastic stops flowing but can still be moved in the channel. High-temperature materials require a distinctly higher threshold than PLA. Pull the filament out in one firm movement. On the tip you will see a cast of the inside of the channel together with all the dirt. Repeat until the tip comes out clean and perfectly conical.
For clearing the hole use a needle thinner than the hole, and do it only with the nozzle hot. A drill bit of the nozzle diameter reams the hole out and permanently changes its geometry, so if you reach for a drill bit, treat the nozzle as spent.
Related problems
Clean, properly dried filament of consistent diameter is the cheapest way to prevent clogs. Porima filaments are produced to a ±0.03 mm diameter tolerance, and we publish the manufacturer's full official print data — you don't have to guess it. Our warehouse is near Poznań, in Swarzędz.
See Porima filaments · 3D printing temperature table · All 3D printing problems