Hi Peter, indeed setting the value of the override setpoint to anything other than 0 should do the trick. The override setpoint value is then updated immediately, the actual setpoint is updated a couple of seconds later.
Can you try to enable debug logging as I mentioned earlier ? Because that should show the actual writing to the opentherm gateway and the response from the gateway which should tell us if the command was received succesfully.
To enable debug logging, in short: log in to your device running openhab and SSH into localhost port 8101 (thats the openhab console) with username openhab and password habopen:
$ ssh -p 8101 openhab@localhost
Password: habopen
Then issue the following commands
openhab> log:set DEBUG org.openhab.binding.openthermgateway
openhab> log:tail
This should give you a rolling log screen displaying everything regarding the opentherm gateway binding in high detail. Please look for a combination of something like:
...
Sending message: TT=21
Received message: TT: 21.00
...
This should appear directly after you set the room temperature override value in the UI (or any other way).
To quit the rolling log screen, hit Ctrl + C
You may want to set the loglevel for opentherm gateway binding back to ERROR level to prevent loads of log entries to be generated:
openhab> log:set ERROR org.openhab.binding.openthermgateway
Please let me know what you find.
Regards
Arjen