Clogged nozzle and under-extrusion: find where the blockage is and fix it

How to recognise it

A complete clog is obvious: the printer moves but nothing comes out of the nozzle, or the filament won't load. A partial clog is trickier: lines become thin or uneven, gaps and missing layers appear, and filament extruded by hand doesn't come straight down but curls around the nozzle. Prusa and Bambu Lab both point to curling filament as a typical sign of a partial clog; Bambu adds that it can also distort flow dynamics calibration.

Sound helps: ticking or clicking from the extruder means the motor is skipping steps against too much resistance. If the resistance persists, the gears dig into the filament and turn it into dust, which further reduces grip. Remember, though, that under-extrusion does not always mean a clogged nozzle: Prusa also lists a badly seated nozzle, wrong slicer profiles, misaligned gears and wet or out-of-tolerance filament.

Checks in order: where is the blockage

Work from the simplest check to the most involved. The exact procedures (how to pull the PTFE tube, how to remove the hotend, which temperatures to use) differ between models: always follow your printer's official guide. Caution: the nozzle and heater block are very hot; Bambu Lab recommends heat-resistant gloves and keeping your face away, because pressure built up behind a clog can spray out molten plastic. Before disassembling the extruder or gears, switch the printer off and let it cool, unless the guide explicitly requires a hot hotend.

1. Spool and path: check that the filament is not tangled on the spool and that the PTFE tubes are intact and fully seated. If you use a multi-material unit, Bambu's guide suggests disconnecting it to rule it out.
2. At the specified material temperature, try extruding from the menu. Missing, weak or uneven flow calls for checks of feeding, extruder and hotend; it does not by itself prove a clog.
3. Bambu Lab (X1/P1), Creality (Ender-3 V3): Follow the model’s official diagnosis to distinguish hotend and extruder faults. Remove or disconnect components only under the conditions specified by the manual.
4. PTFE tube: Creality (K1) says to pull the filament out while hot and inspect its tip; a mushroom-shaped bulge means the PTFE tube needs replacing.
5. Extruder: with the hotend removed or disconnected, extrude and retract from the menu. If the filament won't advance or come back, the blockage is in the gears or filament guide: clean dust and residue with a small brush or compressed air and check that the gears are not damaged or skewed.
6. Idler tension: Prusa notes that an idler that is too loose lets the filament slip and one that is too tight grinds it. Adjust it as described in your extruder's manual.

Cleaning: needle, cold pull and heat creep

For a partial clog at the tip, Bambu Lab and Prusa use the cleaning needle supplied with the printer, inserted from below with the nozzle hot. Bambu recommends not pushing it too deep, so molten plastic isn't pushed higher and the clog made harder to clear, and skipping this step with a 0.2 mm nozzle. The stated temperatures differ: Bambu uses 250 °C on the X1/P1 series for PLA, PETG, TPU and ABS, while Prusa gives higher temperatures for PLA and for PETG/ABS on MK3 models. Use the ones in your model's guide.

A cold pull cleans the inside of the nozzle: load filament at printing temperature, let the temperature drop until it is only softened, then pull it out so it takes the residue with it. Bambu recommends doing it after every cleaning and when changing materials, especially before TPU, which is flexible and can't push residue out. Reference temperatures differ between models (for example Bambu gives 100 °C for the X1 series and 70 °C for the P1S with PLA, Prusa 85 °C on the MK3S); Prusa recommends PLA, pulling slowly, steadily and straight up, and advises against cold pulls with some hardened steel nozzles. Repeat until the extracted tip has the nozzle's shape and is clean.

If the problem returns after a few layers, tackle heat creep: Prusa suggests checking that the heatsink fan spins and blows in the right direction, cleaning dust off the fins, making sure the PTFE tube sits flush with the heatbreak, lowering the bed by 5–10 °C, using thicker layers and unloading filament while hot at the end of a print. For PLA on PEI plates, Bambu recommends printing with the door open or top cover removed to keep the chamber cool.

Brand notes

Bambu Lab: the wiki has separate pages for finding which part is clogged, for the hotend and for the extruder, for each series (X1/P1, A1, H2D, H2S, H2C, P2S, X2D). On the H2D, if filament still won't extrude with the hotend removed, the clog is in the extruder and the filament guide must be removed. For filaments loaded with fibres or particles (CF, GF, marble, glitter, glow-in-the-dark) Bambu advises against the 0.2 mm nozzle and against brass or stainless steel nozzles, which clog or wear quickly, and recommends hardened steel nozzles.

Prusa: the «Clogged nozzle/hotend» pages distinguish between a clogged nozzle and a clogged hotend, because the blockage may also be in the PTFE tube or heatsink; on Nextruder printers under-extrusion can also come from a nozzle not pushed fully home or a misaligned gearbox after opening its cover. Prusa notes that PLA in an enclosure above roughly 27 °C ambient may clog. Creality: the K1 and Ender-3 V3 guides start with the spool and gears, use the hot pull-out test and ask you to check that the gears are intact and aligned.

When to replace a part

Replacement is justified only in specific cases. Nozzle: if neither needle nor cold pull restores flow, Prusa says to replace it, because the blockage may be above the tip; also replace it if it gets damaged while cleaning, and expect a brass nozzle to wear if you often print abrasive materials. PTFE tube: when it is deformed or the extracted filament has a mushroom-shaped tip (Creality). Gears or extruder assembly: when they are damaged, deformed or skewed (Creality). After changing the nozzle, recalibrate the first layer as the manufacturer describes. If the part is intact, cleaning, idler adjustment, cold pulls and a cooling check are almost always enough.

How to verify the result

Record the model and variant, material, slicer profile and change made. Repeat the same test and compare the result with a photo taken before the adjustment. Keep the change only if it improves the defect without introducing others. Use your model’s instructions for temperatures, calibration and disassembly; this guide is not based on our own hands-on tests.