Problem solved
To couple the measurements to the right instruments in Domoticz I used their Idx numbers instead of the ID's and now it works!

For others who might struggle with this:
"Set here your own Domoticz ID's" should be: "Set here your own Domoticz Idx nrs"

My problem: Errors when uploading sketch into my Arduina Mega and no values in Domotics. Lately I received my ordered EMS-board from bbqkees (thanks!) and connected all bits and pieces together to read out my Nefit boiler. So far so good... I installed the sketch and the serial monitor shows values ...

How to integrate this project into Domoticz?

Having an EMS level shifter, an Arduino Mega and a working Domoticz installation on my NAS, my next challenge is to integrate the measurements into Domoticz. What's the right setup methode?

I am using a Nefit boiler in combination with the Honeywell Evohome system wiht 8 zones and this works well. Allmost all radiators are fitted with thermostatic valves, in every room at least one with an HR92 controller. Didn't want an Easy thermostat because of exact the same reasons you have. I use ...