HOW TO DIAGNOSE A NOZZLE CLOG

Three different problems produce the same symptoms (extruder clicking, weak or no extrusion): Partial clog: debris partially blocks the nozzle bore. Some plastic still flows but not enough. Full clog: debris fully blocks the nozzle. No plastic flows even when manually pushed. Heat creep: filament softens *above* the melt zone (in the heat break) and jams there. Symptoms identical to a clog but the actual blockage is somewhere different. Fixes are different. Cold-pulling clears partial clogs but does nothing for heat creep. Replacing the nozzle fixes a worn nozzle but not a failed hotend cooling fan. Diagnose first - then you spend 5 minutes fixing instead of 2 hours guessing.

Diagnose when: the extruder is clicking or grinding, extrusion is thin, prints are starting fine then degrading, or the nozzle suddenly stopped extruding entirely. Skip diagnosis and replace nozzle when: you've already done multiple cold pulls and the symptoms persist, or you've printed many hours of abrasive filament on a brass nozzle (worn, not clogged).

Run through these checks in order: 1. When did symptoms start? - Right after switching filament: incompatible material residue. Cold-pull at the higher of the two filaments' temperatures. - After leaving printer hot but idle: carbonised debris. Cold-pull at the appropriate temp. - During a long print (first 30 min fine, then degrades): heat creep. Skip to step 4. - Suddenly during a print, no warning: partial clog or extruder grinding. Continue to step 2. 2. Try manual extrusion at print temp. - Heat to print temp. From the LCD, command 50 mm extrusion. - Filament extrudes cleanly: not a clog. Check extruder tension and gear teeth. - Filament extrudes thin: partial clog. Cold pull (see how-to-do-cold-pull). - Filament doesn't extrude at all: continue to step 3. 3. Check the extruder. - Open the extruder case. Inspect the gear teeth - are they covered in plastic dust? Pellet-shaped pieces of filament? That's grinding. - Pellets means the gear is failing to grip the filament - either the filament is too soft (TPU), the tension is wrong, or the gear teeth are worn. Adjust tension or replace gear. - Clean the gear teeth, push filament through manually with the lever held open. If it pushes through to the nozzle but doesn't come out, it's a full clog. - Full clog: cold-pull aggressively. If still blocked after 5 pulls, replace the nozzle. 4. If symptoms develop over the course of a long print: heat creep diagnosis. - Listen to the hotend cooling fan (the small one *above* the heat break, not the part fan). It should be running constantly during printing. - If you don't hear it or it sounds like it's struggling: failed fan. Replace ($3-10). - If the fan is running but you can feel little air movement: dust blocking the heat sink. Clean. - If both fan and airflow are fine: retraction distance too high pulling softened plastic into the cold zone. Reduce retraction (Bowden 2-3 mm, direct 0.5-1 mm). - If you upgraded to all-metal hotend: PLA at >215C is heat-creep-prone on all-metal. Drop to 205C. 5. Confirm the diagnosis with a test print. - Print a small object at default settings. - If the cold pull / fan replacement / retraction adjustment fixed it, you diagnosed correctly. - If symptoms return, escalate: nozzle replacement, hotend disassembly, or hardware-level debugging.

Assuming every extrusion problem is a clog. Heat creep, extruder grinding, e-step miscalibration, and worn nozzles all look similar. Diagnose first. Replacing the nozzle without trying cold pulls. A new nozzle costs $1-5 but takes 10 minutes to swap and re-calibrate. Cold pulls cost nothing and take 2 minutes - try first. Skipping the hotend fan check on long-print failures. If symptoms scale with print time, it's heat creep until proven otherwise. Don't fix retraction, don't replace nozzle - check the fan. Ignoring extruder grinding. Pellets near the extruder mean the gear is slipping. Cold-pulls won't help; you need to fix the extruder grip first.

Once diagnosed, jump to the right fix: how-to-do-cold-pull (partial clogs), how-to-change-nozzle (full or worn nozzle), or clogging-heat-creep (heat creep). For broader extrusion troubleshooting, see under-extrusion.