Pipe plot, preliminary draft single-family house 170 m²

Yes, the flow volume is sufficiently low.

So not a defect but a feature

But according to Wikipedia, all systems with more than 3 liters volume must have a circulation pump. This is stated in the [Trinkwasser Verordnung].

Exactly, but it is under 3 liters. Small cross-sections and direct cable routing. The heating system is not located in the basement.

I would have installed the circulation anyway - because it must bother you, otherwise you wouldn't have mentioned it. For me, it would always be a must in the house...

What about the question regarding the decoupling?

The system is decoupled but has its ~42 dB. In between, there is only one door, which, as is well known, does not absorb 42 dB. Hot water: Not much longer than in the rental apartment with circulation; it does not actively disturb, here only expectation and result were compared.

I am not talking about the installation and the advertising promises of Vaillant. Did you place it on a decoupled base or is it standing on the screed/raw floor?