Since there is not much to find about integrating this bath controlling flow in any kind of domotica, is there anybody who already has some experience with the Viega Multiplex Trio E WLAN module integrated in HA?
Spending € 300,- for some trial & error is a bit over my head.
I have a similar question. I have a Viega Floor Heating with the Fonterra Smart Control. I am pondering over whether I should get the WiFi Module. But it would only really makle sense if I can somehow integrate it in Home Assistant. Das anyone have any experiences here?
I know I’m late to the party, but I had one installed in my bathroom so I can perhaps shed light on how it works. I stumbled onto this topic by using Google. I don’t use Home Assistant but Homebridge/Homekit.
I’ve been building a homebridge plugin with a friend to use the WLAN module so it’s perfectly usable in Home Assistant too given the right plugin. Here’s the github repo. It’s still in development as we have some bugs to fix regarding API use.
The WLAN module exposes a simple webserver with a webapp. We analyzed what the app was doing as we used it. The webapp doesn’t require any kind of auth, which is a bit disturbing as basically anyone on your LAN can potentially run a bath 
With it you can :
The plugin needs to regularly “ping” the API in order to keep the water running. Water stops flowing if the ping isn’t happening.
Some controls seem to be missing from the API. We didn’t find out how to detect how much water has been used yet. You apparently can’t set programs like with the physical buttons but you can run them once they’ve been created.
You can also run a test of the whole system and also a hygienic cleanup with hot water.
That’s all I can say for now about it, I hope this’ll help whoever finds this post. 
Thanks so much for making this happen as I was literally looking for this plugin for several years. It is working perfectly. Please let me know where I can donate 
Thank you.
Thomas