Since HA 2025.8 Modbus error

[Stefan-83]

Just updated to 2025.8
Unfortunately "Stiebel Eltron ISG" isn't working anymore. Tried to remove/add the device again.

"Failed setup, will retry: ModbusClientMixin.read_input_registers() got an unexpected keyword argument 'slave'"

It seems to be a problem with Modbus. Are there any changes in the latest update?

Thanks

Version of the custom_component

2025.7.1

[knechtandreas]

I just upgraded to 2025.8 as well and getting this exact same error since the upgrade.

[sommer-nt]

It's also surprising that the same error still appears when I roll back to version 2025.7.4. Has anyone here tried this? What could be causing this?

[pskskp]

In my case, the problem occured when I've upgraded Home Assistant Core. My Stibel Eltron ISG is 2025.7.1. I've tried to install other version but not luck.

[alb-sch]

Same problem here ... like @sommer-nt tried to downgrade to an older version of Home Assistant Core ... no chance. It looks like the upgrade of Home Assistant Core upgrade a python library as well, which is now causing the incompatibility. Does anyone know how to move back to an older version of the Modbus library?

[alb-sch]

Sorry ... @Stefan-83: it looks like parameter "slave" needs to replaced by "unit" ... but I can't any related entry in the code

[sommer-nt]

In the meantime, I deleted the HACS integration of the Stiebel Eltron ISG and tried to get it working again on 2025.7.4. Unfortunately, that failed, as the error popped up again what is really mysteriously. Even with the perfectly working 2025.4.1 (April release) from pail23, I still get the Modbus error. Unfortunately, now I can't integrate the Stiebel Eltron device at all. It looks like the error is deep in the HA core library like @alb-sch mentioned. But I can't identify where exactly the bug is anchored.

[alb-sch]

@sommer-nt: as far as I understand the integration is using a package named "pystiebeleltron". When looking into the source code of that very package you find entries like:

init.py

            heat_pump_data = await self.read_input_registers(
                slave=self._slave,
                address=registerblock.base_address,
                count=registerblock.count,
            )

the slave=self.slave seems to be the problem since it is supposed to be changed into unit=self.slave ... adapting that locally isn't really the problem ... it is just work 😉 . But ...

1. how do I install my local changes within Home Assistant?
2. this could only be a temporary workarround ... how to perform a final fix?

[Rocki75]

Same problem here, after updating to 2025.8.

[sommer-nt]

@alb-sch I'm not a specialist, so unfortunately I can't answer your questions.
Especially since I couldn't find the "pystiebeleltron" package in my integration.
I looked for it in the custom_components under the stiebel_eltron_isg.

[Djcd]

seems like with the update to pymodbus 3.11.0 there were some breaking changes with 3.10.0. To summarize it shortly:

• ModbusSlaveContext replaced by ModbusDeviceContext
• slave=, slaves= replaced by device_id=, device_ids=

I tried my best to open an PR for the pystiebeleltron library. It seems to fix the problem for me, but i don't know if i break something else. I hope the maintainer will support me 😄

[alb-sch]

@Djcd thanks for helping out to get the problem fixed ...

It seems to fix the problem for me

How can we get your fixes?

[jahallam]

I have encountered the same problem when upgrading to 2025.8
Where can I find the file I need to update?

[sommer-nt]

@Djcd Could you please show step by step what you exactly did? I am a bit lost, since I couldn't navigate into the code file where to adjust the certain variables and how to save. Thanks in advance.

[alb-sch]

To all: the Stiebel Eltron ISG Plugin is working for me as well ... thanks to the code provided by @Djcd.

Just in case if anyone wants to know the steps I took ... here they are:

1. copied all of the files provided by @Djcd into a directory name lib/pystiebeleltron located in /config/custom_components/stiebel_eltron_isg, the root directory of the Stiebel Eltron Plugin
   Goal: having a local copy of the fix of @Djcd
2. did a "*grep pystiebeleltron .py" in the /config/custom_components/stiebel_eltron_isg directory and copied all files containing pystiebeleltron in order to have a backup
3. modify each file having the line pystiebeleltron so that e.g.

from pystiebeleltron import (
get_controller_model,
)

in file init.py changed to

from .lib.pystiebeleltron import (
get_controller_model,
)

So I added .lib. in front of pystiebeleltron forcing the pluging to take the local copy of the library. You need to do this for all the files containing "pystiebeleltron"

4. in manifest.json, which should somehow look like

{
"domain": "stiebel_eltron_isg",
"name": "Stiebel Eltron ISG",
"codeowners": [
"@pail23"
],
"config_flow": true,
"documentation": "https://github.com/pail23/stiebel_eltron_isg_component",
"iot_class": "local_polling",
"issue_tracker": "https://github.com/pail23/stiebel_eltron_isg_component/issues",
"requirements": [
"pystiebeleltron>=0.2.0"
],
"version": "2025.7.1"
}

remove the entry "requirements" so that it looks like

{
"domain": "stiebel_eltron_isg",
"name": "Stiebel Eltron ISG",
"codeowners": [
"@pail23"
],
"config_flow": true,
"documentation": "https://github.com/pail23/stiebel_eltron_isg_component",
"iot_class": "local_polling",
"issue_tracker": "https://github.com/pail23/stiebel_eltron_isg_component/issues",
"version": "2025.7.1"
}

DON'T FORGET TO BACKUP THE FILE BEFORE

By removing this line you tell the plugin to use the local copy of the lib.

Now you're ready to reboot. In my case the Stiebel Eltron ISG is available again.

I consider this as a workarround and a dirty change ... but we urgently needed to be able to control our heatpump again 😉

Anyhow ... I hope, that there will be a fix available soon. Thanks for all your efforts.

[Djcd]

thanks @alb-sch for the instructions and sorry for the late answer. I will concentrate to get this fix released, so that this will be working again for all without the hassle. Let's hope the maintainers are happy with my changes 😄