Possible ZHA bug with Zen-01 Thermostat

[Filmetti]

From September 2023 until May of 2025, I used the Zen Zigbee Thermostat without issue. I use ZHA with a Sonoff dongle plus.

In May 2025, I started to have responsiveness issues with the thermostat - commands sent from Home Assistant wouldn’t register on the thermostat, giving this error: “Failed to perform the action climate/set_temperature. Failed to send request: Failed to send request: <Status.NWK_NO_ROUTE: 205>”.

Commands sent from the thermostat, however, would be reflected in Home Assistant immediately. I spent a small amount of time troubleshooting, and then essentially moved to a Venstar T2000 mini. I’ve since had some time to run down the issue with the Zen thermostat, and I’ve become convinced that it’s a bug in ZHA or Home Assistant. Obviously the error indicates that it’s a network/transport issue, but I’m convinced that’s because of software, not hardware or network setup.

Troubleshooting steps I have taken:

1. Upgraded the Sonoff firmware with the HA add-on.
2. Changed zigbee channels. No difference on 20 or 25.
3. Changed 2.4.ghz wifi channels. No difference on 6 or 11.
4. Removed the ZHA integration and all associated data and rebuilt it from scratch.
5. Reinstalled HA and rebuilt my entire system from scratch.
6. Moved the thermostat directly next to the Sonoff dongle. LQI is now 255, but the problem persists.
7. Switched to Zigbee2MQTT - the thermostat works perfectly under Z2M, but unfortunately the thermostat card that is paired with the thermostat under Z2M is terrible, and I haven’t found a way to fix/customize it yet.

So here’s where I am now: The thermostat is set up in a test-bench scenario directly next to the zigbee dongle. If I remove it and then reconnect it, it will work perfectly for anywhere from 5 minutes to an hour, and then sent commands stop working. Commands sent from the thermostat to HA are reflected immediately, and the indicator on the thermostat shows that it’s connected to the zigbee network.

My three theories as to the root cause are:

1. HA update changed something
2. ZHA update changed something
3. HA pushed a firmware update to the thermostat which caused an incompatibility. I’m currently showing firmware 0x0000021f, which is not the firmware version format I’ve seen other places.

My guess is that it’s a ZHA update, but I’m not sure.

Does anyone have any ideas about what might be happening? Any other Zen thermostat users with this problem? I don’t like the Venstar (the temperature sensor is very jumpy and inaccurate), so I’d like to get back to using the Zen at some point.

If needed, I do have some debug logs that ran while having this communication issue. I'm happy to do more debug-level logging (with some assistance). I asked this same question on the HA Community Discord and got basically no responses, but also asked it in the forum and found 2 other people have the same issue. I don't feel like this is specific-enough yet to open an issue, so I thought a discussion would be appropriate.

Thanks!

[TheJulianJES]

Do you have source routing enabled in your configuration.yaml?

[Filmetti]

I don't believe so, no - the default in ZHA is Table Routing, correct? Also this is a very small network - just 5-6 devices, so no real need to reduce network overhead.

[Hedda]

Troubleshooting steps I have taken ...

Are you connecting your Zigbee Coordinator USB radio adapter via a relativly long USB-extension-cable as well as moved it away a bit from your computer running Home Assistant and all electronics (especially USB 3.0 devices and appliances with WiFi) or possible other sources of EMF/RMI/RMI including power-supplies/cables? That is, are you folliwng these best practice tips that includes this which you did not mention:

• https://community.home-assistant.io/t/zigbee-network-optimization-a-how-to-guide-for-avoiding-radio-frequency-interference-adding-zigbee-router-devices-repeaters-extenders-to-get-a-stable-zigbee-network-mesh-with-best-possible-range-and-coverage-by-fully-utilizing-zigbee-mesh-networking/515752

PS: FYI, EMF/RMI/RMI interference can practically jam/block Zigbee messages to the Zigbee Coordinator USB radio adapter which is why it is so important to connect it via USB-extension-cable so that you can physically move it away from other electronics. See example in this video:

• https://www.youtube.com/watch?v=tHqZhNcFEvA

[Filmetti]

Yes, it's on a 6-foot extension and away from sources of interference. Also, as mentioned in my post, the thermostat is directly next to the coordinator, the LQI is 255, and the thermostat functions perfectly under Zigbee2MQTT. So I don't think interference is an issue here.

[ConorIA]

I was getting no route, and it turned out the Zen was trying to connect via a ZigBee Smart Plug / router that had been unplugged. I replugged the router and re-interviewee the thermostat. That made it "work" for a minute, but it erred with "No Ack".

Now however it is failing again with no route and when I look at the network map it is floating around with no connection to any other nodes.

[Filmetti]

That's an interesting thought. As far as I know, though, the only device I have that's capable of routing is my adapter/coordinator. It's a small network with just 5 devices: the adapter, two buttons, one sensor, and the thermostat.

I have definitely had the same network display though, just floating with no connection. Even when commands from the thermostat were reaching HA immediately.

[cburton216]

Having the same issue since the same time frame, same hardware. I mainly use the HA phone app from my local network to interact with the thermostat. Ive observed the following behaviors:

-No consistency in time of day for the issue occurring, which may rule out RF (was just a suspicion on my end.)

-If I try multiple commands from the thermostat card, and then I wake up the thermostat display by physically touching it so it illuminates, the commands still dont go through. Only when I interact with the display after waking it up, then all the commands go through in quick succession

-If I turn off my phones wifi and then open up the HA app to connect through Nabu, there is a greater chance of the commands going through but not a 100% success rate

-hitting multiple commands on the thermostat card at times kicks commands through, though this is very inconsistent

-restarting HA and/or the server sometimes wake up the thermostat and commands will go through, but this is also inconsistent

-reconfiguring the thermostat exhibits the same behavior as sending it commands, it will not reconfigure until I physically wake up the device

I wish I had a solution, but that is beyond my skillset, so I hope these observations help someone find a fix. Really annoying issue.

[Filmetti]

Thanks for the response - most of that is consistent with my experience, though I haven't collected any data around responses when the screen is off/on. Since this (and everywhere else I've posted) has had minimal response so far, I'm going to add this as a bug report/issue, and then maybe we can start the process of getting this solved.