The AMS won't unload filament: it won't leave the extruder, won't return to the AMS or «filament broken in the toolhead»
Guide based on the manufacturer's official documentation; usi3d has not yet verified it on a machine.
Technology: FDM · Brand: Bambu Lab · Symptoms: The multi-material system fails (does not load, cut or jams), The printer shows an error code or message, Clogged nozzle or hotend · Updated on 9 October 2026
Symptom
When unloading or changing colour, the AMS stops with an alert: it cannot pull the filament out of the extruder (0700-8003), cannot return it to the AMS (0700-8004, «Failed to pull back the filament from the toolhead to AMS») or HMS says that a slot's filament may be broken in the toolhead (0700-2000-0002-0004 and similar).
Likely causes, from most to least likely
- Clogged extruder or too much unloading resistance: the filament does not leave the toolhead.
- A piece of filament has stayed next to the extruder sensor, or the sensor magnet does not spring back, so the printer believes there is still filament.
- Toolhead PTFE tube bent too sharply or debris built up in the AMS internal hub, slowing the filament on its way back.
- The spool does not rotate backwards, or turns slower than the AMS pulls: the active support shaft is not fully inserted or that slot's feeder is failing.
- Broken filament inside the AMS internal hub or a faulty hub sensor (the slot LED stays red).
- Hard filaments such as PLA-CF, which are harder to unload from the AMS.
Checks to tell which one it is
- Release the PTFE tube from its coupler (press the ring) and pull the filament by hand: if it will not come out, it is stuck in the extruder; if it comes out easily, the issue is unloading resistance.
- Look at the green extruder dot in Bambu Studio (device tab) or, on the X series, on the temperature and axis screen: if it stays green with no filament, there is a broken piece in the extruder or the sensor is not springing back.
- Watch the spool while unloading: it should turn backwards; if it stays still and the feeder hums, check that slot's support shaft.
- Look at the slot LED: if the filament has already left the feeder but the LED stays solid red, there is broken filament in the internal hub or its sensor is faulty.
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
Update the firmware and remove sharp bends
Update the firmware first: Bambu Lab fixed unloading failures in recent versions. Then keep the toolhead PTFE tube free of sharp bends; Bambu Lab offers a tube bracket that mounts above the toolhead.
Check: Unloading finishes without an alert.
If that does not fix it: Check the extruder (next step).
If the filament won't leave the extruder
If pulling by hand does not get the filament out, the extruder is clogged: switch the printer off and clean it following the extruder maintenance guide for your model (on the X1 and P1 it has to be removed and the debris cleared).
Check: The filament comes out whole and the extruder dot turns white.
If that does not fix it: If the dot stays green with no filament, check the sensor (next step).
Remove the broken piece and check the extruder sensor
With the printer off, remove the filament detection switch following the guide for your model, take out the broken filament and check that the magnet springs back by itself. On the H2D these sensors sit on the dual extruder idlers.
Check: With no filament the dot turns white; with filament, green.
If that does not fix it: If the magnet does not spring back or the sensor does not respond, contact Bambu Lab support.
Clean the AMS internal hub
If the slot LED stays red with the filament out, or after long use there is debris inside, dismantle and clean the AMS internal hub following the Bambu Lab guide and remove any broken pieces.
Check: The LED goes off when the filament is removed and unloading reaches the AMS.
If that does not fix it: If the hub sensor keeps failing, contact Bambu Lab support.
Make sure the spool turns backwards
If only the yellow feeder gear turns while the black support shaft stays still, push the active support shaft until it is fully seated in the AMS. If the spool turns but slower than the unload, swap the feeder with another slot's: if the fault moves with it, that feeder is faulty.
Check: The spool rewinds at the same pace as the unload.
If that does not fix it: If it happens in several slots, record a video and contact Bambu Lab support.
Hard filaments
If it only fails with PLA-CF or another hard filament, print it from the rear spool holder instead of the AMS.
Check: Other filaments unload normally from the AMS.
If that does not fix it: Contact Bambu Lab support with the printer logs.
Prevention
- Keep the firmware up to date.
- Do not let the toolhead PTFE tube form sharp bends.
- After long use, clean the AMS internal hub: built-up debris increases resistance.
- Use dry filament: brittle filament snaps inside the toolhead.
Still not fixed?
Tell usi3d's AI about your case: choose your printer, describe what you see and add photos if you like. It proposes checks step by step, with their sources.
Printers it applies to
Bambu Lab's FDM printers: A1, A1 mini, A2L, H2C, H2D, H2D Pro, H2S, P1P, P1S, P2S, X1, X1 Carbon, X1E and X2D.
Official sources
This guide summarises the official documentation linked here:
This guide is general information: usi3d has summarised it from the official documentation linked here, and it may not match your model, its version or its firmware. If in doubt, follow the manual and the support of your printer's manufacturer. You decide what you do with your machine, and working on it may affect its warranty.