Clogged nozzle and hotend — the complete fix guide

A clogged nozzle is the second-most-common reason a printer that used to work suddenly doesn't. The fix is almost always one of three procedures: a cold pull (free, 10 minutes), a nozzle change (cheap, 15 minutes), or a hotend rebuild (last resort). Knowing which one you need is the entire skill.

Diagnose: clog vs heat creep vs something else

Before you tear into the hotend, rule out look-alikes:

The cold pull (atomic pull)

The standard procedure for clearing a partial clog without disassembly. Works on every FDM hotend.

1. Remove current filament. Heat hotend, retract, unload.
2. Heat hotend to 250 °C (240 for hotends rated lower). Higher temps melt anything organic still inside.
3. Insert cleaning filament — ideally nylon or cleaning filament (eSun, Polymaker). PLA also works in a pinch. Push 50 mm by hand or via extruder.
4. Drop hotend temperature to 90 °C for PLA cleaning filament; 130 °C for nylon. Continue gently pushing filament as it cools so it bonds to the gunk inside.
5. At target temp, yank the filament out fast in one motion. You should see a darkened plug of solidified plastic on the tip with bits of the old clog stuck to it.
6. Inspect the tip. Nozzle-shaped plug = clean nozzle. Misshapen / has chunks = still clogged. Repeat 2–3 times until the tip comes out a clean nozzle shape.
7. Reload your normal filament and test extrude. If extrusion is normal, you're done.

Nozzle swap

If cold pulls don't fix it, the nozzle's threads or orifice may be permanently fouled. Nozzles cost $2–$10 each — cheaper than the time you'll spend trying to clear a stubborn one.

1. Heat hotend to printing temperature for whatever filament is in it. This is critical — cold nozzles strip the heater block threads.
2. Retract filament.
3. Hold the heater block with one wrench so you don't torque the thermistor / heater cartridge wires loose.
4. Loosen the nozzle with a properly-fitting socket (usually 6 or 7 mm). Don't use a crescent wrench — rounded flats ruin nozzles fast.
5. Remove old nozzle, insert new one. Hand-tight to start.
6. Tighten while hot to firm (~2 Nm). Don't overtighten — the threads are soft brass on most nozzles.
7. Re-level Z-offset — new nozzles sit microscopically differently.

Full hotend disassembly

Last resort, only when filament is wedged in the heat break (the narrow tube above the nozzle) and won't budge.

1. Remove the entire hotend assembly from the printer.
2. Heat it externally with a heat gun to filament melt temperature.
3. Use a 1.75 mm drill bit (by hand, not powered) or a fine wire to push the clog through and out the nozzle.
4. Wipe internal threads with a brass brush (steel will damage them).
5. Reassemble with fresh thermal paste on the thermistor / heater cartridge if your hotend uses it.

Prevention

• Dry abrasive and engineering filaments. Wet nylon and PC eat nozzles from the inside.
• Use a hardened steel nozzle for abrasive filament (carbon-fibre, glow-in-the-dark, wood-filled, metal-filled). Brass nozzles wear out in 10–50 hours on abrasives.
• Never leave a printer hot at idle with filament loaded — PLA carbonises after ~30 min at 200 °C with no flow.
• Clean the bowden / extruder path regularly; bits of broken PTFE can be sucked into the hotend.
• Swap nozzles after 500 print hours on brass, 5000+ on hardened steel.
• Avoid generic-brand cheap nozzles — they wear unevenly and clog more often.

Nozzle types — quick reference

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