Underfloor heating, room thermostats and cold tiles

Also an example, the children's room should be between 18 and 20°, the thermostat was set just under 20°, room temperature was at 26°...

Well, that already sounds like it could be the bathroom thermostat that you turned up.

Well, that already sounds like it could be the bathroom thermostat that you turned up.

No, the thing with the children's room was before, that's why the whole thing happened.

@Perlenmann
Great, I will do that, thank you very much!

You do have a warranty, right?

Because something must be wrong!

Quickly report it to the heating specialist; he should fix it within 4 weeks - later it can get unpleasant for you

So, unfortunately forgot to post the solution to the puzzle here:

It was partly as suspected that the terminals were swapped here: office, child's room, and bathroom.
In another case, the thing wasn’t connected at all (ground on the thermostat was not connected).

You really wonder if anything is checked nowadays at all, or if they just wait for the builder to complain and then fix it piece by piece...

Well, at least it’s warm now.

Thanks to everyone for the support, when you approach completely clueless they just present excuses anyway.

Regards
Stephan

Nice to hear! Even my "remote diagnosis" was spot on.