The electrician has placed the phase on the blue wire

I measured with a voltmeter and with a phase tester. There are 230 V on the blue wire. I have already asked the electrician what is going on. Apparently, at 4 out of 11 connections for the roller shutter motors, he made "a mistake" and wired it incorrectly. This can't be true, can it? In general, we have had quite a lot of bad luck with the craftsmen on our construction project, and our site manager does not show up on site and does not check how the work is being done. Sewage pipes were not laid according to the drawing, therefore no floor-level shower with continuous tiles; the tiler "forgot" in the evening that the bathroom door opens outwards, even though we had discussed with 4 people in the morning what he had to watch out for... If we were not constantly on site, they probably would have built a different house...

Ok, that's annoying. Then you can of course only demand a repair. At the end of the electrical installation, it is checked whether everything is okay. If you have a bad feeling, go to another electrician, explain the problem, and ask for an E-Check. They will then check your installation again. It does cost a few euros, but then you have certainty. Of course, that also does not detect color-switched wires. Nevertheless, I wish you that the further course goes better.

It's not quite that simple. First, you have to determine how many wires are needed and how many are actually installed. If, as I suspect, there are partially too few wires installed (which is why the blue wire is used as a phase), new cables will probably have to be installed. And whether this is still easily possible (keyword wallpapering) is uncertain... The electrician will probably hardly take responsibility for consequential damages...

Now everyone who keeps the DIN VDE standards under their pillow will stone me. But if I have the choice between: A) opening walls, drilling, milling, etc. and laying new cables (with everything that comes with it, i.e. costs/possibly legal disputes) and B) having everything properly measured to check if all protective devices and residual current circuit breakers work, etc., and living with the fact that not everything is 100% installed but technically meets the minimum requirements, then I would definitely choose option B, especially right before moving in. You can still negotiate with the electrician and reduce the bill to have at least some compensation.