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Clogged nozzles and heat creep: cold pulls, needle cleaning and chamber heat

Published October 15, 202616 sources

Short answer

For a partial clog, where some filament still flows, Prusa and Bambu Lab both recommend a cold pull with PLA [3, 6]. A full jam needs heat plus a cleaning needle or fresh filament pushed through first [1]. Repeated PLA clogs in an enclosed printer usually mean heat creep: open the door or top cover, and keep the chamber at least 10 °C below the filament's glass transition temperature [9].

Partial clog, full clog or heat creep

Prusa separates two situations: a clogged nozzle and a clogged hotend. Material can jam above the nozzle, for example in the PTFE tube, so replacing the nozzle does not fix every clog [2]. Partial clogs often show up mid-print even after loading and unloading worked [2]. Heat creep is a third case: heat travels up into the cold side of the hotend, the filament softens and swells there, and the extruder jams [9].

Symptom Likely cause What to check
Nothing comes out of the nozzle Full clog in the nozzle or higher up in the hotend Push-through test, then PTFE tube [2]
Extruded filament curls and sticks to the nozzle Partial clog from debris or particles Needle cleaning, then cold pull [6]
Thin lines, gaps and missing layers mid-print Partial clog Cold pull [1]
Loud clicking from the extruder Nozzle clogged or deformed; a light click points to the gears Nozzle first, then gearing [1]
PLA prints start well, then fail in an enclosed printer Heat creep Chamber temperature, door, plate type [9]
Repeated clogs with carbon fiber, glow-in-the-dark or sparkle filament Particles blocking the tip Nozzle size and material [6]
Clog right after switching from PC or PA-CF to PLA, PETG or TPU Unpurged high-temperature residue Hot purge procedure [8]
Filament flattened inside the extruder Chamber too hot, or very soft filament such as TPU 85A or damp PVA Extruder clog, not the nozzle [8]

Safety before you start

Safety: Bambu Lab requires heat-resistant gloves and asks you to keep your head and face away from the nozzle, because pressure behind a clog can suddenly spray molten filament [6]. Prusa warns that heated hotend parts cause severe burns and says to heat the nozzle only from the printer’s menu, never with an external heat source [1].

Safety: before taking apart the hotend or touching toolhead wiring, Bambu Lab says to power off and unplug the printer to avoid short circuits [11]. Prusa requires the printer to be fully cooled and switched off before checking nozzle seating [13].

Clearing a clog step by step

  1. Unload and get access. Remove the filament and raise the toolhead so the nozzle is easy to reach [2].
  2. Clean the tip with a pin. Bambu Lab heats to 250 °C for PLA, PETG, TPU or ABS and moves the supplied pin through the tip a few times, without pushing it deep, since that drives molten filament higher; it skips this step on 0.2 mm nozzles [6]. Prusa inserts a 0.3–0.35 mm needle 1–2 cm from below, never from the top [2].
  3. Push new filament through. Prusa sets 260 °C after PLA or 280 °C after higher-temperature materials such as PETG or ASA, waits two minutes, then pushes fresh filament in. No flow means the blockage is further up and the nozzle most likely needs replacing [1].
  4. Pull a stuck strand. If filament is visible at the top of the nozzle tube, Prusa grips it with needle-nose pliers at 280 °C and draws it up slowly [1].
  5. Scrape fiber residue. After filled filaments, Bambu Lab heats the hotend to 250–280 °C, scrapes the inside with a metal tool such as an Allen key, flushes with regular filament, and confirms flow with PLA at 220 °C [8].
  6. Finish with a cold pull. Bambu Lab recommends one after every cleaning procedure [6].

Cold pull temperatures by printer

A cold pull fills the nozzle with PLA, lets it cool until it holds the nozzle’s shape, then pulls it out with the debris attached. Each guide uses different temperatures:

Printer Heat and fill Pull at Notes
Prusa MK4/S, MK3.9/S, XL (manual) 270 °C, keep pushing until about 170 °C 100 °C Automatic mode cools to 36 °C, then pulls at 80 °C [3]
Prusa CORE One, CORE One L 270 °C 100 °C manual, 80 °C automatic [4]
Prusa MK3/S, MK2.5/S, MK3.5/S 270 °C, cool to room temperature Reheat to 85 °C [5]
Bambu Lab X1 and P1 220 °C (PLA) 100 °C, screen retract plus a gentle pull [6]
Bambu Lab P1S 230 °C (PLA), extrude while cooling until the extruder skips 70 °C [7]

A good pull carries an imprint of the nozzle on its tip and no dark marks or old color; repeat until it comes out clean [3]. Prusa notes that a cold pull is unlikely to work when fresh filament cannot be pushed through at all, though it still suggests trying the automatic version [1].

Heat creep in enclosed printers

Bambu Lab recommends keeping the enclosure at least 10 °C below the filament’s glass transition temperature. PLA clogs most often because it has the lowest glass transition temperature; TPU is also susceptible, and PETG is affected when the chamber approaches its glass transition temperature [9]. A hot bed heats the chamber: on the P1S, PLA on the Textured PEI Plate needs a 55 °C bed, so Bambu Lab advises opening the front door or removing the top cover. The Cool Plate at 35 °C lets PLA print closed [9]. Its filament guide generalizes this: for filaments softening below 60 °C, such as PLA, PVA and TPU, open the door or remove the glass cover once the bed is above 45 °C [10]. OrcaSlicer’s Softening temperature setting triggers the same warning when the bed reaches that value [14].

Prusa reports that with its enclosure closed and the room above 27 °C, the inside can get too hot for PLA [13]. It also recommends checking that the hotend fan is oriented correctly and not blocked by stray filament [12]. See the PLA guide for other material limits.

Abrasive and filled filaments

Bambu Lab’s filament guide lists a hardened steel nozzle as required for PLA-CF/GF, PLA Glow, PETG-CF, ABS-GF, PA-CF/GF and PET-CF/GF, and marks those filaments as incompatible with a 0.2 mm nozzle [10]. For fiber-filled filament it recommends 0.6 or 0.8 mm nozzles and frequent cleaning [8]. Prusa specifies at least 0.6 mm for Woodfill and a hardened nozzle for carbon fiber or kevlar blends [12], and Polymaker flags its glow-in-the-dark filaments as abrasive, needing a hardened nozzle [16]. More detail is in carbon fiber filaments.

Habits that prevent clogs

  • Load a new filament at the previous, hotter filament’s temperature so it pushes the old material out [12].
  • After high-temperature filaments, Bambu Lab heats to 250–300 °C, retracts, purges with the new filament, then extrudes while cooling to 220–240 °C [8].
  • Avoid long retractions: Bambu Lab generally recommends 2 mm or less because longer settings can cause clogging [15]. See retraction calibration.
  • Use the slicer profile that matches the nozzle, since a standard profile on a high-flow nozzle (or the reverse) can cause severe under-extrusion or clogs [1].
  • Store filament dry; wet filament can swell and bubble in the hotend [1].

Questions

Which filament works best for a cold pull?

Prusa's testing found PLA works best because other filaments tear or melt too much and do not keep the nozzle's shape [3]. Bambu Lab uses PLA in its examples but says nylon, ABS or ASA can also be used at suitable temperatures [7].

Can I cold pull every nozzle type?

No. Prusa says not to cold pull a Nozzle X and to use cleaning filament instead [3]. Its acupuncture-needle method also does not apply to high-flow nozzles because of their internal geometry [1].

Why clean the hotend before switching to TPU?

Bambu Lab recommends a cold pull before printing TPU after regular filament, because flexible TPU may not push residue out of the hotend and can clog on it [7].

Sources

  1. Clogged nozzle (CORE One, CORE One L, XL, MK4/S, MK3.9/S). Prusa Knowledge Base. Manufacturer documentation. Partial clog signs, clicking, needle and push-through methods, heat creep prevention, safety. Accessed October 12, 2026.
  2. Clogged nozzle/hotend (MK3.5/S, MK3S+, MK2.5S). Prusa Knowledge Base. Manufacturer documentation. Clogged hotend vs clogged nozzle; early signs; forcing a clog out. Accessed October 12, 2026.
  3. Cold pull (MK4S, MK4, MK3.9S, MK3.9, MK3.5, MK3.5S, XL). Prusa Knowledge Base. Manufacturer documentation. Automatic and manual cold pull temperatures; PLA preferred; Nozzle X exception. Accessed October 12, 2026.
  4. Cold Pull (CORE One, CORE One L). Prusa Knowledge Base. Manufacturer documentation. Automatic and manual cold pull on CORE One. Accessed October 12, 2026.
  5. Cold pull (MK3/S, MK2.5/S, MK3.5/S). Prusa Knowledge Base. Manufacturer documentation. Cool to room temperature, reheat to 85 °C, pull. Accessed October 12, 2026.
  6. Nozzle/Hotend Unclogging Procedure for X1/P1. Bambu Lab Wiki. Manufacturer documentation. Clog causes, pin cleaning at 250 °C, cold pull at 220/100 °C, glove warning. Accessed October 12, 2026.
  7. What is a Cold Pull and how is it performed?. Bambu Lab Wiki. Manufacturer documentation. P1S cold pull at 230/70 °C; other filaments; cold pull before TPU. Accessed October 12, 2026.
  8. Nozzle Clogging. Bambu Lab Wiki. Manufacturer documentation. Extruder vs nozzle clogs, fiber-filled residue cleaning, switching from high-temperature filament. Accessed October 12, 2026.
  9. Heat creep. Bambu Lab Wiki. Manufacturer documentation. Mechanism, 10 °C below glass transition rule, door and top cover guidance by plate. Accessed October 12, 2026.
  10. Filament guide: printer, nozzle, AMS, build plate, glue compatibility and required parameters. Bambu Lab Wiki. Manufacturer documentation. Hardened nozzle requirements; chamber control by softening temperature. Accessed October 12, 2026.
  11. Troubleshooting Steps if Filament Not Extruding. Bambu Lab Wiki. Manufacturer documentation. Power off before maintenance; clog locations. Accessed October 12, 2026.
  12. Under-extrusion. Prusa Knowledge Base. Manufacturer documentation. Hotend fan checks, heat creep in enclosures, nozzle needs for filled filaments, loading temperature. Accessed October 12, 2026.
  13. Under-extrusion (Nextruder printers). Prusa Knowledge Base. Manufacturer documentation. PLA in a closed enclosure above 27 °C ambient. Accessed October 12, 2026.
  14. Material Basic Information. OrcaSlicer Wiki. Slicer documentation. Softening temperature setting and door warning. Accessed October 12, 2026.
  15. Stringing and Oozing. Bambu Lab Wiki. Manufacturer documentation. Retraction length above 2 mm can cause clogging. Accessed October 12, 2026.
  16. Polymaker Material Print Tips. Polymaker Wiki. Manufacturer documentation. Glow-in-the-dark filaments are abrasive and need a hardened nozzle. Accessed October 12, 2026.