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Bambu Lab: printer stopped working after firmware upgrade / can't start prints anymore

Bambu Lab: printer stopped working after firmware upgrade / can't start prints anymore


If your Bambu Lab printer stopped working with SimplyPrint after a firmware update, the cause is almost always Bambu's Authorization Control System (ACS). ACS prevents third-party software (us, OrcaSlicer, Home Assistant, all of them) from starting prints, heating the printer, or sending movement commands when the printer is in Cloud mode.


The good news: SimplyPrint still works with Bambu Lab printers on the latest firmware. You just need to switch the printer to LAN-only Mode with Developer Mode enabled. This article lists your options, in the order we recommend them.


Background reading on what ACS is and why Bambu shipped it: Bambu Lab security firmware "Authorization Control System" update.


What changed


The latest firmware for every current Bambu Lab printer ships with ACS. SimplyPrint can still connect and read status, but write actions (start print, set temperatures, move axes) are blocked when the printer is in Cloud mode. Switching the printer to LAN-only Mode with Developer Mode enabled is the supported way to get full functionality back.



This is the path Bambu themselves point to and the one we recommend for everyone going forward.


  • Restores full SimplyPrint functionality (start prints, AMS control, temperature control, movement).
  • You keep your printer on current firmware and continue to get Bambu Lab's latest features and fixes.
  • You lose Bambu Handy and OTA firmware updates over the cloud, but our firmware-update guide covers the offline path and a quick mode-toggle workaround.


How to enable both modes: Bambu Lab: LAN-only mode and Developer Mode - how to enable.


Option 2: downgrade to older firmware (if you'd rather stay on Cloud mode)


If you specifically want to keep using Cloud mode (e.g. you rely on Bambu Handy, or you don't want to deal with the bridge LAN-only setup), you can downgrade the printer's firmware to a version released before ACS.


Downgrade targets per model:


  • X1 / X1C / X1E - to anything older than 01.07.00.00
  • P1P / P1S - to anything older than 01.07.00.00
  • A1 / A1 Mini - to anything older than 01.03.00.00
  • H2D - not possible. ACS shipped from day one on H2D.
  • P2 series - not possible. ACS shipped from day one.


Step-by-step: Bambu Lab: how to downgrade firmware.


Downgrading is an escape hatch, not a long-term plan. The pool of users who can run old Cloud-mode firmware is shrinking, and newer AMS units may eventually require newer printer firmware than your downgrade target supports.


Option 3: X1Plus open-source firmware (X1 series only)


If you own an X1 / X1C and are comfortable with custom firmware, X1Plus is unaffected by ACS and works with SimplyPrint without restrictions. This is a community project, not officially supported by Bambu Lab.


Project page: X1Plus on GitHub.





Updated on: 25/05/2026

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