Replacing a Siemens RAA21

I have a floor heating system with a Siemens RAA21 thermostat in each room.

I have two wires coming to my current Siemens thermostats (in the "L" and "Y1").

How do I transfer these connections to a Tado thermostat? L to COM and Y1 to NO?

I don't have a neutral wire coming in on the Siemens, but I don't think it's useful for a Tado thermostat, is that right ?

Many thanks.


  • Yes, that's probably correct. I replaced an RAA20 and wired it that way but i did submit my details to Tado who gave me customised installation instructions for my system. Have you done that yet?