OH 4 - MQTT no longer working after update from OH 3.4

Hi All.

I updated yesterday from OH3.4 to OH4.0.3.
Now the previously working MQTT connections are no longer working. I am using MQTT Actions within Rules with Blockly and I am not able to send anything anymore. Was working with OH3.4.

Nothing changed on my MQTT broker side.
I am using the MQTT Binding from OpenHab, Bridge Config - Settings are ok.
I do not see any errors, any error messages, the binding is not offline, the MQTT Server can be pinged.

Any ideas?

Should I be able to see in the events.log when a MQTT message was sent?

I am using OpenHab 4.0.3, on a raspb4
(updated from 3.4 this morning, since it wasn’t working with 3.4 as well).
using the Aeotec Z-Stick Gen5
The MQTT broker is Mosquitto, installed on a different server.

I don’t think there are any logs created when using the publishMQTT action unless there is a problem that generates an exception.

The MQTT Broker Thing is showing as ONLINE?

How are you monitoring the MQTT message traffic?

The OH 3.4 instance is for sure not still running? If it is, did you change the client ID on the MQTT Broker Thing? You cannot have more than one client with the same name connected to a broker at the same time.

There were no breaking changes to the MQTT binding between 3.4 and 4.0.

In the tags for you post you mention Blockly. Did you open and resave all your rules as the OH 4 list of breaking changes described?

Thanks for your answer.

Yes, I am monitoring the MQQT traffic. I don’t see anything send from OH towards my MQYY broker.

I am using Blockly with the MQTT action, this is actually where I see it breaks.
Where is this “list of breaking changes”?


maybe its too simple to be true for you too, but i pretty much had the same expect for me everything is running on the same machine. Did you restart all services and mosquitto too?

Mine was the same, everything was fine, except openhab not to connect to mosquitto initially anymore.


The release notes has the list of breaking changes and what to do about them. The Blockly docs also discusses what you need to do. Rules Blockly | openHAB

Awesome. Thanks a lot.

That was the solution.