AMS-HT run-to-zero behavior (documentation gap)

Bambu Lab P Series Troubleshooting
1

I’m looking for confirmation and/or official clarification on AMS-HT behavior when a spool is fully consumed during a long active print, specifically around filament authority, reload timing, and pause states.

This is not a basic “how do I change filament” question, this is about running spools to true zero without wasting material, and understanding whether the observed behavior is intentional and safe, or just tolerated.

Observed behavior (repeatable)

Hardware / software:

  • P1S

  • AMS-HT (single-spool)

  • Bambu Studio (desktop)

  • Printing ASA / PETG / PA (behavior consistent across materials)

When an AMS-HT spool runs out during an active print:

  1. Runout is detected at the AMS-HT feeder inlet

    • Studio reports “No filament”

    • Printer often continues printing for some time using filament still in:

      • AMS-HT internal path

      • Rear PTFE

      • Printer PTFE / extruder / hotend

  2. AMS-HT can be opened and a new spool loaded immediately

    • Even though filament still exists downstream

    • AMS-HT advances the new filament a short, fixed distance

    • Filament appears to be parked (not continuously fed)

  3. Load / Unload operations remain locked

    • Printer status shows “Printing, unable to operate”

    • This persists even if extrusion has stopped

    • Pausing on the printer UI alone does not always release control

  4. Authority release sometimes requires a “double pause”

    • First pause: printer UI (or auto-pause on extrusion loss)

    • Second pause: explicitly pressing Pause again in Bambu Studio

    • Only after this does status change to “Paused”

    • Only then does Load Filament (AMS-HT) become available

  5. Issuing Load Filament from Bambu Studio works reliably

    • Load from printer UI is inconsistent

    • Load from Bambu Handy often remains locked or laggy

    • Studio appears to be the authoritative control surface

Once this sequence is followed, the print resumes normally with no layer shift.

Mental model that seems to match reality

  • AMS-HT “empty” means no upstream supply, not “path is clear”

  • AMS-HT may still contain filament internally after runout

  • During active printing:

    • Printer owns downstream filament

    • AMS-HT feed authority is locked

  • New filament insertion causes a short pre-feed / parking action, not a full feed

  • Continuous feeding only occurs after:

    1. True pause (authority released)

    2. Explicit Load command

This appears intentional, but it is not documented anywhere. :frowning:

Questions for confirmation

  1. Is this run-to-zero + staged reload workflow expected and safe when done with the correct pause/authority sequence?

  2. Is the double-pause requirement (printer + Studio) intentional, or a UI/firmware edge case?

  3. Is Bambu Studio the recommended interface for AMS-HT recovery during active prints?

  4. Is there an internal concept of:

    • “HT-paused” vs “user-paused” states

    • or filament authority states that are not exposed in the UI?

Why this matters

AMS-HT is often used for:

  • Long prints

  • Expensive filaments

  • Moisture-sensitive materials

Discarding 10–15% of a spool to avoid runout is not always reasonable.
Understanding the correct workflow matters for both material cost and print reliability.

Request

If this workflow is:

  • unsupported → it would be helpful to know

  • supported → it should be documented

  • tolerated but risky → guidance on material-specific risks would help

Appreciate any clarification from Bambu staff or experienced AMS-HT users.

Thank you!

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