Floor Heating Thermostat for COSMO water RTL system

Hi all,

I am looking for a controllable thermostat for my COSMO water rtl sub floor heating valve.
I have already contacted COSMO but they did not have a solution for me (the answer did not seem very competent tbh).
Maybe there is an adapter to connect a regular wall thermostat?

Maybe somewhere here knows a solution!

It’s unclear what you’re looking for, what do you mean by “controllable”, and what do you consider a “regular” wall thermostat ?
Any solution is highly dependant on the mechanical and remaining heating control components, which is different in different installations, systems and countries (and you didn’t even mention where you live, I assume DE ?).
So shouldn’t you be asking that from your local HVAC guy (den Heizungsinstallateur) or some do-it-yourself HVAC forum ? How does your question relate to openHAB at all ?

I would like to have a openHAB2 compatible mechanism to control the pictured valve. So looking for hardware recommendation. I don’t mind if it is z-wave, 433mhz or any other protocol but it should work with openHAB.

I do live in Germany yes.

Thanks for the tip to search for a HVAC guy/forum, will check into that!

You could try the MAX! series. I have some of those thermostats and the connector looks the same, they also come with 3 adapters. There’s a thermometer in the thermostat, but a separate wall thermometer is also available.
To control MAX!, you need the MAX!cube, and with that one, you can also control them from openHAB. Get a starter kit.
But don’t blame me if it’s not compatible, hard to tell based on just a picture.

Thanks for the recommendation. I was actually looking into the MAX! system.

It seems that the RTL system means that the temperature is measured inside the thermostat and the heat is transmitted via the metal plate (it’s a plate not that small “knob” on regular wall thermostats).

However, could you post a picture of the adapters? I can’t find it on the internet right now.


That what the MAX! thermostats will do, or if you add a wall thermostat (room controller), that where it’ll measure room temperature.

No. Order them, try them, and return them if they don’t fit.


long time ago since the last post here. But I am currently looking for the same “issue”.
Afaik RTL thermostats are completely different because they measure the water temperature which is going through the floor heating pipe (not the air temperature). This is important because my heating engineer told me that you might destroy your floor tiles or burn your feet when water more than 40 degree (approx; I dont remember the exact figure) is sent through the pipe.

But I am interested if you testet the MAX! thermostast or others back in 2016 or if you found another solution to controll a RTL floor heating?

Just a few days ago I was also looking for an integration of my floor heating into OH.
I thought I could exchange the RTL with a normal thermostat, but as you have already mentioned, this is not really a good idea as the temp has to be limited to avoid damage and pain :roll_eyes:

So you would need a device as shown here
One is a RTL and the second one a standard thermostat.
For me this is too expensive for an OH integration only, so I left it as it is.

No, I didn’t end up doing this. It became clear that these thermostats are totally different and will not work even with adapter. I have dropped the idea for now. I considered to add an external motor to the existing manual valve. May do that with my new 3d printer when the winter comes…

Here we are in 2024 and still no one seems to sell RTL valve with Z-Wave, ZigBee, whatever battery powered :frowning:

(I have wall radiators in bathrooms, from which the returning water goes through floor without isolation - so kind of floor heating and hence the RTL instead of standard TRV.)

It would be nice if I could heat up my bathroom before I wake up and keep it down for the rest of the day :slight_smile: