NOZZLE CLOGGING AND HEAT CREEP

The extruder clicks or grinds while the motor turns, no plastic comes out of the nozzle, or extrusion starts fine but degrades over the course of a long print.

A clog is a physical blockage somewhere along the filament path from extruder to nozzle tip. Carbonised plastic builds up in the nozzle from leaving the printer hot without extruding, dust gets dragged in with the filament, or you switched filaments without purging fully and incompatible materials solidified together inside the nozzle. The result is reduced cross-sectional area for plastic flow - the extruder pushes harder and harder until the gear slips. Heat creep is different and often misdiagnosed as a clog. Above the nozzle is a heat break - a thin metal section designed to be cold so filament arrives at the melt zone solid and stays solid above the melt zone. A small fan blows on the heat break to keep it cold. If that fan fails or its airflow is blocked, heat from the nozzle creeps up the heat break and softens the filament where it should be solid. The softened filament expands inside the heat break, jams against the walls, and stops being pushable. Symptoms look identical to a clog but the actual blockage is in the wrong place. The diagnostic difference matters because the fixes are opposite. A regular clog is fixed by cold-pulling and tweaking nozzle settings. Heat creep is fixed by cooling the upper hotend - replacing the fan, adding airflow, or reducing retraction (every retraction pulls already-softened filament further into the cold zone where it cools and jams).

Based on 150 confirmed fixes from r/FixMyPrint, these are the causes ranked by how often they actually worked: 1. Cold pull cleared a partial clog - the most-confirmed fix. Even users certain their nozzle was clean discovered debris on cold-pull tips. 2. Hotend cooling fan failed or blocked - fan replacement or clearing dust from the heat-sink restored heat-creep-prone printers to normal. 3. Retraction distance too high (heat creep cause) - dropping from 5+ mm to 2-3 mm prevented filament from being pulled into the cold zone repeatedly. 4. Nozzle worn out (especially with abrasive filaments) - replacing brass nozzles after 100-200 hours of carbon-fibre or glow-in-dark printing fixed chronic under-extrusion. 5. All-metal hotend running PLA too hot - all-metal hotends are sensitive to PLA heat creep above 215C. Dropping to 205C and ensuring fan airflow fixed it. Data sourced from r/FixMyPrint - one of the largest 3D printing troubleshooting communities on Reddit. This represents real user-reported issues and community-confirmed fixes, not theoretical advice.

If clog appears after the printer sat hot without printing for a while - carbonised debris from holding temperature. Cold pull. If clog only appears on long prints (and not short ones at the same settings) - heat creep. The first 10-30 minutes are fine; degradation builds over time. Check the hotend cooling fan first. If clog appears immediately after switching filament - incompatible materials mixed inside. Cold pull at the higher of the two filament's temperatures. If extrusion is consistently low across many prints - worn nozzle (especially if printing abrasive). Replace. If you can hear the hotend cooling fan running but feel little air movement - fan is failing or blocked. Replace or clear obstruction. If the issue started after upgrading to an all-metal hotend - stock retraction settings cause heat creep on all-metal. Reduce retraction distance.

Cause 1: Cold pull Heat to print temp, push filament through manually until clean. Drop to 90C (PLA) or 100C (PETG/ABS). Pull firmly in one fast motion. Repeat 3-5 times. The pulled tip should be shaped like the nozzle interior with debris attached. If cold pulls don't clear it after 5 attempts, follow with a needle clear (0.4 mm acupuncture needle from below while pushing filament from above). Cause 2: Replace hotend cooling fan Unplug the small 30-40 mm fan above the heat break (not the part fan). Test by powering the printer on - the fan should spin immediately at full speed. If it doesn't, replace ($3-10). Common failure on Ender 3s after 1000+ hours. Check that intake isn't blocked by a dust shroud or cable. Cause 3: Reduce retraction distance If you're getting heat creep on all-metal, drop retraction to 2-3 mm (Bowden) or 0.5-1 mm (direct drive). Less filament gets pulled into the heat break per retraction = less cold-zone softening. Combine with reduced retraction frequency by increasing 'minimum extrusion distance' to 1.5-2 mm. Cause 4: Replace nozzle Heat hotend to print temp, unscrew nozzle (never cold - you'll damage threads). Brass: $1-5, fine for PLA/PETG/ABS, replace every 200-500 hours. Hardened steel: $10-20, mandatory for carbon fibre / glow / abrasive blends, lasts 1500+ hours. Re-tighten new nozzle hot after the printer has been at temperature for 5 minutes. Cause 5: Lower temperature on all-metal hotends All-metal hotends transfer more heat upward than PTFE-lined hotends. Drop PLA to 200-205C, PETG to 230-235C. Make sure the heat break is airflow-cooled and the fan duct isn't crooked.

Bowden printers (Ender 3 family): Stock PTFE-lined hotends are clog-resistant up to 240C; above that the PTFE degrades and creates clogs from chemical breakdown. Don't print PETG / ABS at 250C+ on a stock Ender hotend - upgrade to all-metal first. The hotend cooling fan is a common failure point - replace if you hear bearing noise. Direct drive printers (Bambu, Prusa MK4S): Bambu hotends are robust but heat creep happens if the chamber gets too hot during long prints. Crack the door for PLA. Prusa MK4S has a quick-swap hotend - swap to a new one as a diagnostic instead of cold-pulling. Enclosed printers (Bambu P1S, K1 Max): Heat creep risk is significantly higher in enclosed chambers because the hotend cooling fan is pulling warmer air. For PLA in an enclosed printer, vent the door. ABS doesn't have heat creep issues in an enclosure because the materials are designed for the temperature.

PLA / PLA+: Most heat-creep-prone because of low softening point. Sensitive to all-metal hotend overheating. Cold pulls easy at 90C. PETG: Sticky, hard to cold-pull. Use 100C cold pull temp. Less heat-creep-prone than PLA because it stays flexible at higher temperatures. ABS / ASA: Easiest to cold pull. Heat creep only an issue if the cooling fan fails entirely. TPU: Heat-creep-prone because soft TPU squishes inside the heat break under retraction pressure. Use minimal retraction (0.5-1 mm) and slow print speeds. Carbon fibre / glow / metal-fill: Wear brass nozzles fast. Replace with hardened steel or you'll have chronic under-extrusion within a dozen hours.

Cold pull every 200 hours of printing as preventative maintenance. Catches developing partial clogs before they fail mid-print. Replace the hotend cooling fan every 1000 hours or at first sign of bearing noise. They're cheap and a failed one will cost you dozens of failed prints. Don't leave the printer hot without extruding for more than a few minutes between prints. Cool down between sessions to prevent carbonisation. For abrasive filaments, install a hardened steel nozzle and never go back to brass for those materials.

Use FixMyPrint to get retraction distance, nozzle temperature, and hardware checks tuned for your specific printer and filament - based on what actually worked for similar issues in the community. Go to /settings-generator to generate yours.