Symptom: the filament is standing still and the extruder gives out a loud click or knock every few seconds. The head goes on tracing paths, except that nothing is left on the print. Once the print is stopped the filament will not retract, and when you try to push it through by hand you feel hard resistance rather than the material giving softly.
A filament jam is a blockage of the material somewhere on its way from the spool to the nozzle. The click you hear is the moment the drive gear skips over the filament because it cannot move it. It is worth establishing straight away where the blockage lies, because the remedy is completely different for each section. Take the filament out of the extruder and try pushing it through the tube alone by hand, then separately push a short piece through the hot hotend. This simple split settles the matter in a minute and saves an hour of dismantling.
Most common causes and fixes
1. The filament has snapped inside the Bowden tube
The broken-off piece stays in the tube and blocks the rest. This happens most often after a longer break in printing, when the spool has been sitting unpacked, and with materials that are stiff by nature. The symptom is misleading: the extruder feeds material, the length counter goes up, and nothing happens at the nozzle, because the driven section is simply pressing against the obstruction.
How to check: disconnect the tube at both ends and look through it against the light. If you cannot see a clear bore, the obstruction is inside.
What to do: push the fragment out with a new piece of filament introduced from the extruder end, and if that does not help, push it through with a thinner rod. Then deal with the cause: brittleness comes from storage. Keep spools in sealed containers and do not leave filament tensioned around a sharp bend in the tube, because that is where it breaks most often.
2. A knot on the spool
The classic trap. The end of the filament released loose during rewinding slips under an adjacent winding and forms a slip loop. As long as the printer is drawing material from the top, everything works. When it reaches the tangled spot, resistance rises abruptly and the feeder starts clicking. The preceding symptom is the spool jerking and a marked increase in extruder noise for a quarter of an hour or so before it stops.
How to check: look at the spool while printing. If it turns in jerks rather than smoothly, or you can see a tensioned length running under other windings, you have your answer.
What to do: stop the print, untangle the windings by hand and rewind the material. As a precaution, never release the free end of the filament; always clip it into the hole on the rim of the spool. Also check that the spool turns easily on its holder, because resistance at the holder increases the force needed to unwind and encourages the loop to tighten. We cover this in more detail on the tangled filament on the spool page.
3. The filament diameter falls outside tolerance
Filament that is too thick does not fit freely in the tube and in the hotend channel, so resistance builds up along the length of the path. Filament that is too thin gives an apparently opposite symptom, but ends the same way: the drive gear loses its grip on it, the material slips, and in a moment a groove is worn that blocks the feed. Ovality is just as dangerous as a diameter deviation, because in one plane the material rubs and in the other there is no grip.
How to check: measure a dozen or so points along a metre with callipers, turning the filament 90° each time. Note the largest and the smallest value, because it is the spread that tells the truth, not a single measurement.
What to do: set material with a large spread aside for less demanding jobs, or make a claim. Porima filaments are produced to a ±0.03 mm tolerance, which means predictable resistance in the tube and a stable knurl grip along the whole length of the spool.
4. Extruder tension is set wrongly
Too little tension means slipping and clicking at even slight resistance. Too much drives the knurl teeth deep into the plastic, deforms the cross-section and creates a thickened spot that will not pass any further. With soft materials it is worse still: TPU under excessive tension simply bulges out sideways and leaves the path between the knurl and the bearing.
How to check: pull the filament out and inspect the section that passed through the extruder. Shallow, even tooth marks are fine. A deep groove or flattening means too much tension, or a blockage further along in the hotend.
What to do: set the lowest tension at which the material does not slip during normal printing. TPU Flex 98A requires a markedly gentler setting than PLA and works best in a direct drive, because in a Bowden setup soft material coils up in the tube instead of pushing through it.
| Porima material | Nozzle | Feeding note |
|---|---|---|
| PLA and PLA variants | 200–260 °C depending on variant | Trouble-free material, standard tension |
| PETG | 240–260 °C | Soft in the transition zone, avoid excessive tension |
| HT PETG | 270–300 °C | High temperature, an all-metal path with no PTFE tube in the hot zone is required |
| ABS / ASA | 250–280 °C | Moisture-sensitive, always dry before printing |
| PA (nylon) | 260–290 °C | Absorbs water very quickly, drying mandatory |
| TPU Flex 98A | 230–260 °C | Direct drive recommended, slow feeding, low tension |
| PLA/CF | 220–250 °C | Abrasive, requires a hardened nozzle |
Source: the official FDM technical data table from the manufacturer, Porima. The full listing: 3D printing temperature table.
5. The filament softens above the melt zone
If heat from the heater block travels higher than it should, the material softens at a point where the channel is at full diameter. It expands, sticks to the wall and creates an obstruction that the extruder can neither push through nor retract. This is the most common cause of jams that appear after the first hour of printing, or right after a longer pause with the nozzle hot.
How to check: pull the filament out after a failed attempt and inspect the tip. A thickened spot shaped like a droplet, or a neck a few centimetres above the melted part, is this fault's signature.
What to do: look after hotend cooling and make sure the nozzle is not left hot needlessly. We describe this mechanism in detail on the clogged nozzle page. In a closed chamber for ABS or ASA, feed the hotend fan air from outside the chamber.
6. The filament is damp
Wet material swells, and steam causes uneven flow which the feeder reads as resistance. With nylon and TPU a few days in the open air are enough for printing to start jamming. The manufacturer specifies drying nylon as mandatory.
What to do: dry the spool according to the recommendation for the material: PA 8–12 h at 65–80 °C, ABS and ASA 6–12 h at 40–60 °C, HT PETG 6–12 h at 50–60 °C, PLA and PETG 2–4 h at 30–40 °C, TPU Flex 98A 2–4 h at 40–60 °C. You will find a practical guide on the filament drying page.
Quick checklist
- Split the problem: the tube separately, the hotend separately.
- Inspect the spool for a tangled winding and check that it turns freely.
- Pull the filament out and assess the shape of the tip and the knurl tooth marks.
- Measure the diameter with callipers at a dozen or so points, turning the filament.
- Set the lowest effective extruder tension.
- Check the hotend fan and that the heatsink is clear.
- Dry the material if it is PA, TPU, ABS, ASA or HT PETG.
The overriding rule: change one parameter at a time. After every change run the same feeding test before returning to the actual print.
How to remove jammed filament without damaging the hotend
Never pull cold filament by force, because the most common result is breaking it off in exactly the worst place, that is at the constriction. Heat the hotend to the printing temperature of the material in question and only then try first to push the material downwards, to release it from the walls, and then to retract it in one smooth movement. If the filament will not give, loosen the extruder tension so that you are not working against your own drive.
When a broken-off piece stays in the channel, take the hotend apart hot. Always hold the heater block with a spanner, because twisting the assembly without support can tear off the heater or the thermistor. After reassembly run several cold pull cycles until the tip you draw out comes away clean.
Related problems
An even diameter and a properly wound spool eliminate most jams before they arise. 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