Why is my Bambu Lab printer offline?

Bambu Lab printers connect to SimplyPrint through the SimplyPrint Client, a small app on a computer or Raspberry Pi on your network. When a Bambu Lab printer shows offline, the Client usually knows why. This guide starts there, then walks through the network, the access code, file transfers that get stuck on "Download", and printers that flicker.

Quick reference

Start here: run Diagnose in the Client

1. On the computer or Pi that runs the Client, open http://localhost:8000. From another computer, open http://<device-ip>:8000.
2. • If the page doesn't load, try 8001, 8002 and so on. When another program already uses port 8000, the Client starts on the next free port.
2. Click Printers and find the printer. Its card shows the status the Client sees.
3. If the printer is not online, click Diagnose on its card. The Client tests the connection and says what is wrong.

Check: read the result and follow the matching section:

Before anything else, make sure the Client is up to date (Settings > About > Check). Older versions had connection bugs, such as Bambu printers failing to connect over MQTT, that are fixed now. See How to update the SimplyPrint Client.

The Client isn't running

1. Check the device that runs the Client is on and awake.
2. • Windows: look for the SimplyPrint icon in the system tray.
   • Mac: look for the SimplyPrint icon in the menu bar.
   • Linux or Raspberry Pi: run systemctl status simplyprint-client.
   • Docker: run docker ps and look for simplyprint-client.
2. Start it if it isn't running, or restart the device.
3. Windows: if the Client won't start or keeps disappearing, check whether your antivirus quarantined it. Restore it, add an exception for the Client's folder (C:\Program Files\SimplyPrint Client), then reinstall it as in How to install the SimplyPrint Client.

Check: the Client opens in your browser and lists your printers.

Turn off sleep on Windows and Mac computers that run the Client. A sleeping computer takes every printer offline.

The printer's IP address or Wi-Fi changed

This is the most common reason a printer that worked goes offline.

1. Power cycle the printer: turn it off, wait 30 seconds, turn it on, and wait for it to join the Wi-Fi.
2. On the printer's screen, find its current IP address in the network settings.
3. In the Client, click Edit on the printer's card. If IP address is different, enter the new one and click Save changes.
4. In your router, give the printer a fixed IP address or a DHCP reservation.

Check: the printer shows online in the Client and in SimplyPrint.

Why step 4 matters: the Client follows IP changes through announcements the printer sends on the local network. If those are blocked, or missed, the Client keeps trying the old address until you fix it or restart the Client. A fixed address removes the problem.

Wi-Fi with several access points (mesh). A printer can roam to an access point with a weak signal and drop out, again and again. Move the access point closer, or lock the printer to one strong access point in your router or mesh settings.

Different networks. The Client and the printer must be able to reach each other. A guest network or a separate VLAN often blocks that. Put them on the same network, or allow the ports below between them.

Rule out the network. Install Bambu Studio on the same computer as the Client and connect to the printer in LAN mode. If Bambu Studio can't reach it either, or ping <printer-ip> fails, the problem is the network or the printer, not SimplyPrint.

Access code, serial number and LAN mode

For full control, the printer needs LAN-only Mode and Developer Mode turned on. See Bambu Lab: LAN-only mode and Developer Mode - how to enable.

1. On the printer's screen, find the access code (in the LAN mode or network settings) and the serial number (in the device settings).
2. In the Client, click Edit on the printer's card and compare Access code. Enter it exactly as the screen shows it, then click Save changes.
3. If the serial number doesn't match, remove the printer from the Client and add it again, then link it to the existing printer in SimplyPrint. See Manage the SimplyPrint Client.

Check: run Diagnose again. It says Bambu credentials are verified or Printer is reachable.

After a firmware update, check both modes again and power cycle the printer. See Bambu Lab: printer stopped working after firmware upgrade.

Prints stuck on "Download"

The printer is online, but a print never gets past Download, or fails with an error about the file transfer. The Client sends files to Bambu Lab printers over FTPS, and that connection is blocked or busy.

1. Make sure a USB stick or microSD card is in the printer. In LAN-only mode, files go to that storage.
2. Restart the printer, especially if you just turned on LAN-only mode. Some printers need a restart before file transfers work.
3. Restart the computer or Pi that runs the Client.
4. If you have a firewall between the Client and the printer, allow port 990 (sometimes 989) and the data ports around 50000-50100.

Check: start the print again from SimplyPrint. It moves past Download and starts printing.

Errors like "421 There are too many connections" or "SSL: WRONG_VERSION_NUMBER" usually clear after you restart both the printer and the device that runs the Client.

The printer flickers

The printer switches between online and offline every few seconds or minutes.

1. Make sure only one Client runs. Two Clients connected to the same printer, for example an old Raspberry Pi still switched on after you moved to a new computer, or the old Bambu Lab client next to the new Client, fight over the connection. Switch off or uninstall the extra one.
2. Rule out other apps connected to the printer. Home Assistant's Bambu Lab integration, Bambuddy, other farm tools, and Bambu Studio or OrcaSlicer left open on the printer's LAN connection each hold their own connection to the printer, and the printer only accepts so many. Close them, or switch them off for an hour. If the printer then stays online, turn them back on one at a time to find the one that clashes.

Check: the printer stays online for several minutes.

Online in the Client, offline in SimplyPrint

The Client reaches the printer, but SimplyPrint doesn't hear from the Client.

1. Check the device that runs the Client has internet access.
2. If you are on a company or school network, give IT the network requirements. The Client needs to reach SimplyPrint.
3. Update the Client, then restart it from the status menu in the bottom-left corner.

Check: the printer comes online in SimplyPrint.

If a printer still shows Printing while it is offline, that is the last state SimplyPrint knew. It updates as soon as the printer is back online.

Ports the Client uses

Only needed if a firewall sits between the Client and the printer:

Still offline?

Download the Client's logs (Logs > download icon > Select all > Download) and send the .zip with your printer model, firmware version and Client version. See Manage the SimplyPrint Client: download the logs.

Related articles

• Why is my printer offline?
• Manage the SimplyPrint Client: logs, password, backups and printers
• How to update the SimplyPrint Client
• Bambu Lab integration: LAN-only vs Bambu Cloud
• Bambu Lab: LAN-only mode and Developer Mode - how to enable
• Connecting Bambu Lab printers to SimplyPrint

Updated on: 27/10/2026