Communication between boiler and room thermostat

[ra-kal]

Hi,

pls can somebody explain me the meaning of the data sent between the boiler and thermostat?

I have Vaillant boiler and eRelax thermostat. The boiler was supported automatically, but I had to add a configuration for the eRelax thermostat, which identifies as SCC. Now my goal is to understand the communication between the boiler and the thermostat in order I can remove the thermostat and control the boiler directly from HA directly.

2025-01-10 11:55:31.656 [update notice] received poll-read bai currenterror QQ=10: -;-;-;-;-
2025-01-10 11:55:31.937 [update notice] received poll-read SCC currenterror02: -;-;-;-;-
2025-01-10 11:55:32.228 [update notice] received poll-read SCC currenterror03: 31;-;-;-;-
2025-01-10 11:55:32.522 [update notice] received poll-read SCC currenterror04: -;-;-;-;-
2025-01-10 11:55:33.604 [update notice] received poll-read SCC ReadModeSCC: 40.31;12;0.0;31;0;0
2025-01-10 11:55:33.875 [update notice] received read bai Status01 QQ=10: 40.0;40.0;-;-;37.5;off
2025-01-10 11:55:34.148 [update notice] received update-write bai SetMode QQ=10: auto;0.0;-;-;1;0;0;0;0;0
...
2025-01-10 11:56:00.805 [update notice] received poll-read bai Status02 QQ=10: on;60;75.0;70;65.0

I understand that the thermostat (SCC) commands the boiler (bai) using SetMode to set Flow temperature target value and possibly other values.

But I'm a lost with the poll-read SCC messages. Are these readings initiated by the boiler? And what is the direction of the information?

The Flags1 value in the ReadModeSCC almost looks like a status of the boiler, rather than the thermostat. Eg. it changes depending on what the boiler is actually doing.

[netweaver1970]

most people would agree that controlling the boiler directly is not always a good idea, unless you have a very good understanding how to set the the Flow temp/duration/timing based on all your house parameters (thermal mass, outside temperature), total heat wanted etc... The thermostat I have (Bulex Migo) is re-evaluating the house' heating control PIR values every 12 heat/cool cycles.

I also went the eBusd route, thinking that I would build this multi-zone super/duper heating system. But that idea died off quickly.

Now I control the Migo thermostat using the Vaillant integration. That takes care of outside temperature compensation, pre-heating etc... Probably you're way smarter than me but I gave up, seeing the trouble in getting the PIR values right, getting correct weather compensation baked in, etc...

My eBusd is now only for monitoring flow/return parameters and some other less important parameters.
A bit sad but one has to chose his battles. And this was the project (rabbithole) too many.

But thank you for trying to decypher the SCC messages, my Migo also identfies as a SCC, but I had not file for it. I had to go the HA-Internet-Migo-Boiler route instead of the HA-Migo-Boiler as ideally wanted.

[ra-kal]

I have an eRelax thermostat in my living room controling the boiler and Zigbee thremostat valves in other rooms. This works somehow, but it is not ideal. If the living room reaches the set temperature, the boiler switches off even the other rooms have not yet reached the target temperature. I could imagine to force the boiler switching on by temporarily rising the target temperature, but this would cause other troubles.

My idea is just simple. I want control only the flow temperature based on the outside temperature and the needs from the rooms. I have already implemented room temperature control by switching the Zigbee valves between fully open, fully closed or automatic (controlled by the valve itself) when the temperature is close to the target value.

Regarding SCC, I have found the configuration file here in this forum : john30/ebusd-configuration#313
It only contains the values periodically sent between the boiler and thermostat though and the meaning of the values was not deciphered.