TLDR; I could not update my switch’s firmware and manually applying the firmware update to the ZBT-2 fixed all the issues.
Environment
Home Assistant > 2025.11 but was running the following during the latest troubleshooting
Core 2026.2.3
Supervisor 2026.02.2
Operating System 17.1
HAOS on Proxmox with USB port passthrough
ZBT-2 Adapter running stock 7.4.4.0 build 0 (20250810210330)
Zigbee2MQTT with all the latest updates
Zigbee2MQTT version 2.8.0
commit: unknown
Frontend version 2.8.1
zigbee-herdsman-converters version 25.120.0
zigbee-herdsman version 9.0.2
I have been struggling with getting updates on Inovelli VZM35SN (Blue series Zigbee fan controller) recently. I tried manually uploading the OTA file as well as using the built in updater.
Everytime it would either not start or fail under 10%.
Digging into the logs I saw the adpter was restarting during the update.
zh:ember:ezsp: ERROR Transaction failure; status=ASH_ERROR_TIMEOUTS. Last Frame: [FRAME: ID=52:"SEND_UNICAST" Seq=159 Len=7].
zh:ember:ezsp: ERROR Transaction failure; status=NOT_CONNECTED. Last Frame: [FRAME: ID=52:"SEND_UNICAST" Seq=159 Len=7].
zh:ember:uart:ash: Port closed, error=null
zh:ember:uart:ash: ======== ASH stopped ========
zh:ember:ezsp: ======== EZSP stopped ========
zh:ember: ======== Ember Adapter Stopped ========
z2m: Adapter disconnected, stopping
The ZBT-2 adapter was not prompting for any updates to itself, but I wanted to see what was available as I saw there was version 7.5.1.0 available from Releases · NabuCasa/silabs-firmware-builder · GitHub
I redirected the adapter to a Windows VM and then tried running updates from Install Firmware – Device Toolbox but it would never complete. It would just spin at 0%.
I unplugged the adapter and plugged into a laptop and tried running the update, same behavior. I tried factory resetting the ZBT-2 and running updates, same behavior stuck at 0%.
I then plugged into a linux laptop and installed GitHub - NabuCasa/universal-silabs-flasher: Flashes Silicon Labs radios running EmberZNet or CPC multi-pan firmware and manually flashed the firmware
Commands
#Install the flasher
sudo apt update
sudo apt upgrade
pipx install universal-silabs-flasher
#Get the device ID
ls /dev/serial/by-id
#Should loook like usb-Nabu_Casa_ZBT-2_10BXXXXXXXXX-if00
#Probe the device
universal-silabs-flasher --device /dev/serial/by-id/usb-Nabu_Casa_ZBT-2_10BXXXXXXXXX-if00 probe
#Download the firmware from https://github.com/NabuCasa/silabs-firmware-builder/releases/tag/v2026.02.23 using a browser or curl
#Install
universal-silabs-flasher --device /dev/serial/by-id/usb-Nabu_Casa_ZBT-2_10BXXXXXXXXX-if00 flash --firmware /home/user/Downloads/zbt2_zigbee_ncp_7.5.1.0_None.gbl --allow-cross-flashing
#Check its updated
universal-silabs-flasher --device /dev/serial/by-id/usb-Nabu_Casa_ZBT-2_10BXXXXXXXXX-if00 probe
Command output consolidated
universal-silabs-flasher --device /dev/serial/by-id/usb-Nabu_Casa_ZBT-2_10BXXXXXXXXX-if00 probe
2026-02-24 00:06:31.668 kali universal_silabs_flasher.flasher INFO Probing ApplicationType.GECKO_BOOTLOADER at 115200 baud
2026-02-24 00:06:33.682 kali universal_silabs_flasher.flasher INFO Probing ApplicationType.EZSP at 115200 baud
2026-02-24 00:06:41.200 kali universal_silabs_flasher.flasher INFO Probing ApplicationType.EZSP at 460800 baud
2026-02-24 00:06:42.471 kali universal_silabs_flasher.flasher INFO Detected ApplicationType.EZSP, version '7.4.4.0 build 0 (20250810210330)' (7.4.4.0) at 460800 baudrate (bootloader baudrate None)
2026-02-24 00:06:42.471 kali universal_silabs_flasher.flash INFO Dumping EmberZNet Config
universal-silabs-flasher --device /dev/serial/by-id/usb-Nabu_Casa_ZBT-2_10BXXXXXXXXX-if00 flash --firmware /home/eric/Downloads/zbt2_zigbee_ncp_7.5.1.0_None.gbl --allow-cross-flashing
2026-02-24 01:33:46.737 kali universal_silabs_flasher.flash INFO Extracted GBL metadata: NabuCasaMetadata(metadata_version=2, sdk_version='4.5.0', ezsp_version='7.5.1.0', ot_rcp_version=None, cpc_version=None, fw_type=<FirmwareImageType.ZIGBEE_NCP: 'zigbee_ncp'>, fw_variant=None, baudrate=460800)
zbt2_zigbee_ncp_7.5.1.0_None.gbl [####################################] 100%
universal-silabs-flasher --device /dev/serial/by-id/usb-Nabu_Casa_ZBT-2_10BXXXXXXXXX-if00 probe
2026-02-24 01:37:43.882 kali universal_silabs_flasher.flasher INFO Probing ApplicationType.GECKO_BOOTLOADER at 115200 baud
2026-02-24 01:37:45.894 kali universal_silabs_flasher.flasher INFO Probing ApplicationType.EZSP at 115200 baud
2026-02-24 01:37:53.410 kali universal_silabs_flasher.flasher INFO Probing ApplicationType.EZSP at 460800 baud
2026-02-24 01:37:54.703 kali universal_silabs_flasher.flasher INFO Detected ApplicationType.EZSP, version '7.5.1.0 build 0 (20260224005837)' (7.5.1.0) at 460800 baudrate (bootloader baudrate None)
2026-02-24 01:37:54.703 kali universal_silabs_flasher.flash INFO Dumping EmberZNet Config
Now all the firmware updates to the VZM35SN completed without issues and looks like there are less errors as well as the system being more responsive and less events like motion detection not being missed.