ZBT-2 Failure to connect

Configuration Zigbee
,
1

Dear community,

Over night my ZBT2 controller fails to connect.

I run HA on a local Raspberry pi 5, with the latest version.
Installed Zigbee2MQTT works OK.

My ZBT-2 controller reports:
[13:06:05] INFO: Preparing to start…
[13:06:05] INFO: Socat not enabled
[13:06:05] INFO: Starting Zigbee2MQTT…
Starting Zigbee2MQTT without watchdog.
[2026-01-06 13:06:17] error: zh:ezsp:uart: → Error: Error: {“sequence”:-1} after 10000ms
[2026-01-06 13:06:17] error: zh:ezsp:ezsp: Connection attempt 1 error: Error: Failure to connect
[2026-01-06 13:06:29] error: zh:ezsp:uart: → Error: Error: {“sequence”:1} after 4000ms
[2026-01-06 13:06:29] error: zh:ezsp:uart: -!- break waiting (1)
[2026-01-06 13:06:29] error: zh:ezsp:uart: Can’t send DATA frame (0,0,0): 00000004
[13:12:46] INFO: Preparing to start…
[13:12:46] INFO: Socat not enabled
[13:12:47] INFO: Starting Zigbee2MQTT…
Starting Zigbee2MQTT without watchdog.

First inital thoughts was a bad cable.
Replacing the cable did not resolve the issue

Installed new Firmware on the ZBT2, succeeded without any problem.
However the connect problem persists.

So switched to another RPi5,

  • installed a backup,
  • connected the device.
    No succes.

Anyone any idea how to debug this futher?
Or do I have a faulty antenna ( although I was able to re-image the firmware ).

Best regards
Arjen

2

Can you show your zigbee2mqtt/configuration.yaml please.

3

data_path: /config/zigbee2mqtt
socat:
enabled: false
master: pty,raw,echo=0,link=/tmp/ttyZ2M,mode=777
slave: tcp-listen:8485,keepalive,nodelay,reuseaddr,keepidle=1,keepintvl=1,keepcnt=5
options: “-d -d”
log: false
mqtt: {}
serial:
port: /dev/serial/by-id/usb-Nabu_Casa_ZBT-2_DCB4D90E8264-if00
adapter: ezsp
baudrate: 460800
force_onboarding: false

4

Not sure if it’s related, but you should use ember, here.

5

Switching to ‘ember’ does not start up de integration.
It hangs on logs:
[14:05:40] INFO: Preparing to start…

[14:05:40] INFO: Socat not enabled

[14:05:41] INFO: Starting Zigbee2MQTT…

Starting Zigbee2MQTT without watchdog.

[14:07:47] INFO: Preparing to start…

[14:07:47] INFO: Socat not enabled

[14:07:47] INFO: Starting Zigbee2MQTT…

Starting Zigbee2MQTT without watchdog.

6

Too much power draw from all the USB devices including ZBT-2?

7

Thank you Tommy Long for this suggestion.
However, there is only 1 external device on the RPi 5 with the RPi preferred ( 27w ) power supply.

8

Yeah, I didn’t think so, but thought it worth considering.
Another thing to try is add rtscts: true to the serial config to see if that helps.

9

Thanks for the suggestion, but no result:

[20:00:40] INFO: Preparing to start…
[20:00:40] INFO: Socat not enabled
[20:00:40] INFO: Starting Zigbee2MQTT…
Starting Zigbee2MQTT without watchdog.
[2026-01-06 20:00:52] error: zh:ezsp:uart: → Error: Error: {“sequence”:-1} after 10000ms
[2026-01-06 20:00:52] error: zh:ezsp:ezsp: Connection attempt 1 error: Error: Failure to connect
[2026-01-06 20:01:04] error: zh:ezsp:uart: → Error: Error: {“sequence”:1} after 4000ms
[2026-01-06 20:01:04] error: zh:ezsp:uart: -!- break waiting (1)
[2026-01-06 20:01:04] error: zh:ezsp:uart: Can’t send DATA frame (0,0,0): 00000004.

10

If you were able to do this, then it seems like there is nothing wrong with the ZBT-2 and cable.
As a sanity check, which firmware did you install?

11

From AI, used this suggestion:
To install firmware on the Home Assistant Connect ZBT-2, use the dedicated web-based Device Toolbox, connecting the ZBT-2 to your computer ( Chrome/Edge recommended), selecting “Install Firmware,” choosing either Zigbee or Thread, and following the prompts, which often involves plugging it in, selecting it in the toolbox, and clicking “Install” for automatic flashing and setup within Home Assistant.

The Device Toolbox

12

You definitely need to use adapter: ember as well as the rtscts: true according to the official Z2M docs.
Don’t rely on AI since they are trained on old data and might not be aware that the ZBT-2 exists.

serial:
    adapter: ember
    port: /dev/serial/by-id/usb-Nabu_Casa_ZBT-2_DCB4D90E8264-if00
    baudrate: 460800
    rtscts: true

PS - you sure the integration did not start when switching to ember? “Starting Zigbee2MQTT without watchdog” is pretty normal and you didn’t post any errors after that line.

13

Thanks everyone on the support on this request.
Re-entering the serial as described in the last post, everything is on good order.

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