ᐅ Shower incorrectly installed and part missing during new build by plumber

The move-in date was June 1st. The plumber forgot an in-wall part for the shower. The Grohe shower was purchased by us. He agreed and acknowledged the mistake. Therefore, the finished shower had to be reopened right on time by June 1st. Five weeks later, it is still not completed. The missing part has been installed and the wall sealed again. However, now the shower is leaking. Water continuously runs from the overhead shower and the control valve. The plumber claims it is a design flaw by Grohe. He even wanted to cut into the shower. Oh man. The plumber has made many other mistakes and is quite uncooperative. We still have several defects with him. What are our rights? Especially since it has not been finished even after 4 weeks. We are dealing with the mess, the delay, and have to take time off work, etc. The plumber apparently is not familiar with the shower either. I no longer trust him. If I hadn’t been there on Friday, he would have closed the valve at the bottom with the cover. Water would have flowed into the wall by the liter because he didn’t even think it necessary to apply silicone. The gaps were so large that a finger fit between the shower back panel (one piece) and the control valve. This is crazy. Can I have someone from Grohe inspect this at the plumber’s expense? Some inspections require special tools that the plumber does not have. Currently, we always have to turn off the main water valve to keep it dry. The plumber is willing to cover the repair costs but refuses any further discount despite all the stress.

If the plumber is willing to cover the costs, that’s already great.
Contact Grohe; they probably have installers who are more knowledgeable in detail.

Personally, I understand that you want to get a bit more compensation for your trouble. But the plumber’s offer to cover the costs is good and not something to be taken for granted, especially when dealing with third-party suppliers.

Regarding the additional defects you mentioned, it would be necessary to know exactly what they are in order to comment. In any case, document and raise these issues early on. Then, as in the first case, work together to find a solution (repair by him or replacement at his expense).
PS: Has the invoice already been paid in full?

Classic! He could always blame it on material defects.

Your writing is unfortunately very difficult to read. Please list the additional defects in bullet points.

Regarding the material defect: The shower was already installed and under pressure before it was reassembled. At that point, everything was sealed. On Friday, the problem started. When I came home, the issue was there. He pressed the cover twice into the fresh silicone, causing it to become completely unsealed because everything stuck to it.

Who is responsible for sealing between the fixture and the tile/shower wall? The tiler says it’s the plumber, and vice versa.

Additional defects
The screed dryer connected to the underfloor heating was incorrectly set.
The wrong heater was delivered; it is larger but at the same price and does not fit optimally in our utility room.
The pipe routing for the heating was planned incorrectly. The pipes run at the back in a niche, with the heater in front; the niche was specifically reserved for this. The suggestion came from him. Two weeks before moving in, he says this is not possible due to maintenance issues, etc.
The pressure reducer in the downstairs toilet was not installed. The toilet was provided by us.
Pipes in the utility room were leaking.
The heating was defective because a sensor was inserted too tightly. As a result, liters of water spilled onto our floor. We were not informed, and the water was not cleaned up. It remained there for several days under the laid carpet.
The overhead shower was installed crookedly the first time it was mounted on the wall. The wall had to be opened a second time. We had to uncover all the defects ourselves.
The outdoor sensor was positioned incorrectly — south-facing.

This is what I can think of off the top of my head. There are more, but I need to check my list for those.

We had to make sure everything runs somewhat correctly, but we have no expertise ourselves. I’m really worried that things won’t work properly. The plumber acts as if this is completely normal. The exposed shower below is already installed. I’m wondering how it is sealed behind it.

The plumber also missed installing the plastic parts on both toilets that are supposed to be between the toilet and the mounting bracket. That can’t be right, can it?

When silicone and sealing are mentioned here, I would recommend consulting an expert or at least getting a second opinion from a professional. Silicone is an expansion joint filler and never a waterproof seal. It looks like you have already encountered a careless job.

Report the defects in writing (very important), set a deadline, and request rectification.