Kobra 3 or Kobra S1 with ACE Pro: error 11511, 11512 or 11518 (filament will not feed, will not retract or jams)

Symptom

The Kobra 3 Combo, or the Kobra S1 with the ACE Pro, pauses with code 11511 (on the Kobra 3, «Extrusion abnormal»), 11512 («Retraction abnormal») or 11518 («Filament clogging detected»): the ACE Pro cannot feed or pull back the filament, or a clog is detected. The S1 asks you to retract the filament above the print head before resuming; sometimes, when resuming, the screen reports an unknown consumable («Unknown consumable» or «Unknown Filament»).

Likely causes, from most to least likely

1. The nozzle or hotend is clogged: on the Kobra 3, Anycubic checks this first for 11518. On the S1, filament can also be left broken above the heat sink, under the print head cutter.
2. A broken piece of filament is left in the hub or in the print head's filament break detector.
3. The ACE Pro buffer is dry, badly fitted or does not spring back, or the PTFE tubes are messy or bent too much.
4. The filament is too thin, or it is damp, tangled or has a deformed tip, and the gear cannot grip it.
5. Filament not suitable for the ACE Pro: very hard or brittle, fibre-filled (PLA-CF or GF) or non-official silk, or soft like TPU; TPU 95A and HIPS can be dried in the ACE Pro but not printed from it.
6. Tubes worn by friction or cardboard spools that slip and shed debris; on the S1, also debris in the four-in-one-out hub or a fault in the module that detects the filament going back to the ACE Pro.

Checks to tell which one it is

• Note the code: 11511 (the filament does not advance), 11512 (it does not go back to the ACE Pro) or 11518 (clog).
• Heat the nozzle and try extruding from the screen to find out whether the hotend is clogged.
• Open the print head housing and check for filament left in the break detector or in the tube above the print head.
• Undo the two hub screws and check for broken filament at the merge port.
• Check that the four ACE Pro buffers move smoothly and spring back into place.
• On the S1, if the filament comes back to the tube above the print head but not to the ACE Pro, the problem is in the return path.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Return the filament and resume

   Return the filament until its tip sits inside the PTFE tube: on the Kobra 3, above the hub, with «Materials» and «Return Materials»; on the S1, above the print head, with «ACE1», the filament and «Retract». If one will not retract, press the black pneumatic fitting, pull the tube out and pull the filament out firmly (on the S1, if it is very stiff, cut it first with the print head cutter); push the tube back into the hub and press «Resume Printing».

   Check: Printing resumes without the error coming back.

   If that does not fix it: Clean the hub merge port (next step).

2. Clean the hub merge port

   If it does not resume and the screen reports an unknown consumable, remove the two hub screws with a 2 mm Allen key (2.5 mm on the Kobra 3 Max), pull out any filament left at the merge port, refit the hub tightening the screws and press resume.

   Check: The screen no longer reports an unknown consumable and printing continues.

   If that does not fix it: Check the print head: on the Kobra 3, the next step; on the S1, the one after.

3. Kobra 3: clear the print head break detector

   Open the print head housing and look at the filament break detector. If a piece is left, pull the extruder lever to the right and push that piece into the extruder with a length of filament. Pull the filament out of the top end of the hub so the detector is not triggered, refit the housing and the tube and resume.

   Check: The detector is clear and printing resumes.

   If that does not fix it: Unclog the hotend (step 5).

4. Kobra S1: clear the print head tube and cutter

   Remove the print head housing, unplugging the part cooling fan cable, remove the blue clip, press the quick connector and pull out the PTFE tube. Cut the filament with the cutter and remove it; if needed, undo the cutter screws with a 2 mm Allen key and check for broken filament above the heat sink. Reconnect the tube, the fan cable and the housing, and press resume.

   Check: The tube is clear and printing resumes.

   If that does not fix it: Unclog the hotend (next step).

5. Unclog the hotend

   Heat the nozzle and press extrude (on the Kobra 3, Anycubic's example is 250 °C with PLA; if nothing comes out, remove the PTFE tube and push filament by hand while pressing the extruder lever). If it is still blocked, remove the quick-swap hotend and, holding the throat with heat-proof gloves or pliers, push a length of filament through it (the S1 does this at 150 °C; on the Kobra 3, if not enough, a long 1.5 mm Allen key); finish with the needle through the nozzle (on the S1, at 230 °C).

   Check: The filament comes out of the nozzle cleanly.

   If that does not fix it: If it is still clogged, replace the hotend or contact Anycubic support.

6. Check the ACE Pro buffer

   Check that the four buffers move smoothly, spring back and are not dry, and tidy up the PTFE tubes. If one is fitted incorrectly, remove the screws of the buffer cover (2.5 mm Allen key; the Kobra 3 guide also uses a 2 mm one), make all four match, check that they run smoothly and refit them.

   Check: The four buffers move the same and the error does not return.

   If that does not fix it: On the S1, check the return path (next step); on the Kobra 3, the filament and the tubes (last step).

7. Kobra S1: check the way back to the ACE Pro

   If the filament comes back to the tube above the print head but not to the ACE Pro, something along the path is holding it: straighten that tube if it is bent too much (Anycubic suggests printing a support that holds it on the print head), clean debris out of the four-in-one-out hub and check the module that detects the filament going back to the ACE Pro.

   Check: The filament goes back to the ACE Pro without jamming.

   If that does not fix it: Check the filament, the spools and the tubes (next step).

8. Suitable filament, spools and tubes

   Load compatible filaments into the ACE Pro (PLA, PETG, ABS, ASA, PET, PA, PC, PP) and avoid very hard, brittle, fibre-filled or soft ones such as TPU. Measure the filament: if it is too thin, the gear cannot grip it. Preferably use standard 1 kg plastic spools (Anycubic specifies 195 to 200 mm diameter and 60 to 68 mm width); with cardboard spools, fit the adapter ring. Replace worn tubes.

   Check: Colour changes complete without clog or tangle warnings.

   If that does not fix it: Contact Anycubic support and give them the error code.

Prevention

• Check the ACE Pro tubes for wear from time to time and replace them in good time.
• Do not load fibre-filled, very hard, brittle or soft filaments such as TPU into the ACE Pro; use it for TPU 95A and HIPS only to dry them.
• Use plastic spools, or fit the adapter ring to cardboard ones, to avoid slipping and debris.
• Use dry filament with a stable diameter, and cut off a bent or deformed tip before loading it.
• On the S1, when you refit the hotend check that it is fully seated: otherwise the nozzle can scrape the bed.

Still not fixed?

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Printers it applies to

Anycubic Kobra 3, Kobra 3 V2, Kobra 3 Max and Kobra S1.

Official sources

This guide summarises the official documentation linked here:

• CODE: 11518 Filament clogging detected · Anycubic
• CODE: 11511 Extrusion abnormal · Anycubic
• Kobra S1 - CODE: 11518 - Filament clogging detected · Anycubic
• Kobra 3 Max - CODE: 11518 Filament clogging detected · Anycubic
• Kobra S1 - CODE: 11512 Retraction abnormal · Anycubic
• Notes for ACE Pro · Anycubic