Quick answer
A clogged nozzle or a printer that has stopped extruding almost always comes down to filament that is not melting and flowing freely: a partial blockage in the tip, heat creep softening the filament too early, wet filament, or a hotend temperature set too low. The fast fixes are to heat the hotend and perform a cold pull, clear the tip with a 0.4 mm nozzle needle, and dry your filament. If flow is still inconsistent, inspect the PTFE tube, heatbreak cooling, and extruder gear.
Why nozzles clog and stop extruding
A clog is anything that stops plastic from flowing cleanly through the small nozzle opening. Sometimes it is a full blockage, where burnt filament or debris lodges in the tip and nothing comes out. More often it is partial, where some lines print thin and the extruder clicks as it skips. The usual causes are moisture (wet PLA and PETG steam inside the hotend and leave carbonized specks that seed the next clog), heat creep (heat travels up the heatbreak and softens filament before it reaches the melt zone, common in enclosed printers with low-glass-transition filaments like PLA, PETG and TPU), printing too cold so the filament never fully melts, and a charred or misaligned PTFE tube that restricts the path. Identifying which one you have saves a lot of trial and error.
1. Confirm it is the nozzle and not the extruder
Before you tear anything down, find out where the blockage is. Heat the hotend to printing temperature and gently push filament through by hand. If you feel a hard stop, the hotend is blocked. On a Bambu Lab printer you can enter maintenance mode, set the nozzle to about 170 C and test extrusion with the hotend assembly removed; if the extruder pushes filament smoothly without the hotend in place, the clog is in the hotend and a cold pull is the next step.
2. Heat up and perform a cold pull
A cold pull (atomic pull) drags softened filament and trapped debris back out of the melt zone. Heat the nozzle slightly above the filament’s normal printing temperature so everything inside melts, then drop the target to around 70 C. As it cools, the filament grips the debris; once you reach roughly 70 C, pull the strand straight up and out in one firm motion. For a first cold pull, 70 C is a safe release point because cooler than that can make the filament too soft to bring the gunk with it. Repeat until the tip of the pulled strand comes out clean.
3. Clear the tip with a nozzle needle
For a stubborn full clog, heat the nozzle to printing temperature and push the included cleaning needle (or a 0.4 mm acupuncture needle) up into the opening to dislodge the plug. Work gently and pair it with a cold pull so the loosened debris actually leaves the nozzle rather than getting pushed deeper. Avoid forcing oversized tools into the orifice, which can widen or damage it.
4. Raise your printing temperature
A temperature set too low is one of the most common causes of poor extrusion and recurring clogs, because the filament never fully melts. If you see under-extrusion and clicking, raise the hotend temperature in 5 C steps within the filament’s recommended range. As a rough guide, PLA prints around 190 to 220 C, PETG around 230 to 250 C, and ABS around 240 to 260 C, so check your spool’s label and tune from there.
5. Dry your filament
Moisture is the most overlooked cause of repeat clogs. Wet PLA and PETG flash to steam inside the hotend, creating bubbles that carbonize on the nozzle walls, and each speck becomes a starting point for the next blockage. If filament hisses, pops or prints stringy, dry it: PLA around 45 to 55 C and PETG around 60 to 65 C for 6 to 8 hours in a filament dryer or low oven, then store it sealed with desiccant.
6. Check the PTFE tube and heatbreak cooling
If clogs keep coming back, look at the filament path. A PTFE tube that is charred, deformed or sitting with a gap above the nozzle lets molten plastic pool and harden, restricting flow before it ever reaches the tip. Reseat or replace the tube so it sits flush. Then make sure the heatbreak’s cooling fan is running and unobstructed; weak heatsink cooling causes heat creep, where prints start fine but begin under-extruding 10 to 30 minutes in.
7. Inspect the extruder gear and tension
What looks like a nozzle clog can be a slipping extruder. Open the extruder and clear any ground filament dust packed into the drive gear teeth, since clogged teeth lose grip and cannot push filament. Check the idler tension is firm but not crushing the filament, and confirm the gear turns when you command an extrusion. Clean teeth and correct tension restore consistent feeding.
Frequently asked questions
What temperature should I use to clear a PLA clog?
Heat the nozzle to around 220 C, slightly above normal PLA printing temperature, so the filament inside fully melts before you attempt a needle clear or cold pull.
How do I do a cold pull on a Bambu Lab printer?
Heat the nozzle just above the filament’s printing temperature, then set it to 70 C and let it cool; once it reaches about 70 C, pull the filament straight up and out, and repeat until the strand comes out clean.
Why does my printer start fine then under-extrude after 20 minutes?
That pattern points to heat creep: heat is climbing the heatbreak and softening filament early. Check that the hotend cooling fan runs and the heatsink is clear, and avoid leaving an enclosed chamber too warm for PLA.
When should I just replace the nozzle?
If a cold pull and needle clearing do not restore flow, or the orifice looks worn, oval or has been damaged by a drill bit, swap in a fresh nozzle; they are inexpensive and a worn one will never extrude cleanly.