Nothing Coming Out of the Nozzle (Clogged Nozzle)

Likely causes, most common first

1. Debris or particles stuck at the tipMost common
   Bambu Lab lists debris on the filament or in the extruder, and particles from carbon fiber, glow-in-the-dark and sparkle filaments, as causes of full and partial clogs.
2. Leftover high-temperature materialCommon
   Bambu Lab notes clogs when very different filaments follow each other without a full purge, such as PLA after PC, or TPU after ASA, and gives a transition procedure for going from high to low temperature materials.
3. Heat creepCommon
   Prusa says PLA in a closed enclosure or a warm room can soften above the melt zone and swell. This usually shows as extrusion stopping partway through a print. See Extrusion Stops Partway Through a Print.
4. Wet, degraded or out-of-tolerance filamentCommon
   Prusa lists wet or degraded filament, inconsistent diameter and impurities. Bambu Lab notes filament larger than 1.75 mm can get stuck, and that moisture-sensitive materials such as PA, PC and fiber-filled filaments clog more easily when damp.
5. Printing too cold or too fastOccasional
   Bambu Lab says printing too cold can cause under-melting and clogs, and that very fast printing may not allow enough time to melt, leading to partial clogs.
6. Wrong profile for the nozzle typeOccasional
   Prusa warns that using a standard profile with a High Flow nozzle, or the reverse, causes flow errors on its printers.
7. Damaged or worn nozzleLess common
   Prusa lists a damaged nozzle as a cause and suggests replacing a heavily used or old one rather than cleaning it.

Fix it, one change at a time

1. Find and follow your printer maker's unclogging procedure. Temperatures, tools and access differ by printer. The steps below are the order Prusa and Bambu Lab use; your maker's page wins where it differs. Heat the nozzle only through the printer's menu: Prusa says not to use an external heat source. Bambu Lab says to wear heat-resistant gloves and keep your head and face away, because pressure behind a clog can make molten filament spray out suddenly.
2. Unload the filament and check the extruder. Remove the filament, then check that the drive gears are free of plastic dust and the idler is at its default setting. Prusa starts here, because a slipping extruder can look like a clog.
3. Clear the tip with the cleaning needle. Heat the nozzle through the printer's menu, then push the needle supplied with the printer up into the tip from below. Prusa uses a 0.3 to 0.35 mm needle about 1 to 2 cm deep Maker spec and says this does not apply to its High Flow nozzles; Bambu Lab says not to push too far, which can push molten plastic higher, and to skip this on 0.2 mm nozzles. On a coated or plated nozzle, check its maker's cleaning instructions first; see Hardened Nozzles.
4. Push fresh filament through. Prusa's procedure heats to 260 °C for PLA or 280 °C for PETG and ASA Maker spec on its printers, waits about 2 minutes, then pushes new filament by hand. Then extrude and check for a straight strand. Use the temperatures your maker gives for your printer.
5. Do a cold pull. Filament is loaded hot, cooled until it is just soft, then pulled out with the debris stuck to its end. Bambu Lab's X1 and P1 example uses PLA loaded at 220 °C and pulled at 100 °C Maker spec, helped by a gentle pull, never a hard one, repeated until the end comes out clean. Bambu Lab recommends a cold pull after every cleaning. Use your printer's automatic cold pull if it has one.
6. If filament is stuck higher up (visible at the top of the hotend or in the tube above it), follow your maker's guide for that case. Prusa's newer printers use pliers at 280 °C Maker spec followed by a cold pull; its older printers may need the hotend removed. Prusa notes a clogged hotend is not the same as a clogged nozzle, so a new nozzle does not always fix it.
7. Replace the nozzle if a full clog survives the steps above, or if the nozzle is old or damaged, using your maker's nozzle change procedure. Prusa says to redo first layer calibration after changing a nozzle.
8. Clean the drive gears afterward. Prusa notes clogs leave residue on the gears that reduces grip.

Confirm it is fixed

Extrude by hand again: the strand should flow straight down at an even thickness with no curling. Then print a small test with a solid top layer and check for gaps. To keep it clear, Bambu Lab recommends storing filament sealed, purging properly when changing from high to low temperature materials, and a cold pull at least once a month Maker spec on its printers, especially when switching filament types.

Why it happens

A nozzle opening is usually a fraction of a millimeter across. Anything solid that reaches it and is larger than the hole stays there: a fleck of carbon fiber, a speck of dust carried in on the filament, a crumb of a higher-temperature plastic left over from the last spool that never melts at this spool's temperature. A small blockage narrows the opening, so the plastic squeezes out to one side and curls. A larger one stops it entirely.

Clogs higher in the hotend are different. Filament is meant to stay solid until it reaches the heated zone just above the nozzle. If heat travels up too far, or the filament swells from moisture or is oversized, it softens and jams in the narrow tube above the nozzle, where a needle from below cannot reach. That is why Prusa separates a clogged nozzle from a clogged hotend, and why a cold pull, which pulls the whole plug out from above, works when the needle does not.

Prevention is mostly about what goes into the printer: dry, clean filament of consistent diameter, a hardened nozzle for abrasive filled filaments (see Hardened Nozzles and Abrasive Filaments), a proper purge between very different materials, and the right profile for the nozzle you have.