Terminate construction contract according to construction status

Hello, I hope my question is in the right forum. We are unfortunately building a house without construction supervision and have had a bad experience with the installer who caused significant, partly serious defects. We followed the normal process of a defect notice, granting an extension, and ultimately termination. Since the contractor wanted to install a complete heating package from Buderus, including solar system, storage tank, and everything that belongs to it, and he obtained the entire package from his dealer, we unfortunately paid for the whole package (of course with a surcharge) and he stored the devices in a garage provided. However, from this total package, only the solar system was installed. In addition, one morning when I was not on the construction site, he installed the sewage pipes, which he had to remove again because the Energy Saving Ordinance requires that the outward-facing walls must be plastered windproof. Now the question, Is billing always done according to the construction status in case of termination? Are the pipes that were installed but then removed considered installed? Do I have to keep the heating system or does he have to exchange it?

Is settlement always done based on the construction status in case of termination?

Can you even terminate? Immediate termination is not that easy. You might be liable for damages. Here, a lawyer is the contact person of your choice.

Are installed but removed pipes considered installed?

No, they are not considered installed. Although I don’t understand why they were removed. You will have to explain that.

Do I have to keep the heating system or does he have to exchange it?

Bought, paid for, and delivered (in your garage?). Installation has not yet taken place, so part of the paid heating package still needs to be installed. After termination, you might get money back and have to find a sucker who installs the devices and then provides the warranty.

My tip: First, calmly talk to the installer. Get a construction supervisor/expert. Or in a different order. Termination is always the very last resort because you will likely cause yourself more problems than you hope to solve.

He is also not interested in continuing. I can't help it that the installer bought the entire package. The exterior walls have to be plastered from the inside because of the airtightness.

The exterior walls must be plastered from the inside due to airtightness.

Ok, were there some pipes in the way for the plasterer?

He is also not interested in continuing. I can't help that the installer bought the entire package.

Yes, you did place the order. Otherwise, how else should the complete heating system have been installed if it was not purchased. You have to deal with it now. Sorry. If you can reach an amicable agreement with the installer, that's fine – but you will have to pay for the heating parts.

To be able to say something about that, you probably need to know the type of contract. If billing is done according to the construction status, then it is a general contractor contract? Then the general contractor is your contact person. It's not that simple.

The installer has not carried out the defect rectification and why should I pay for a heating system that he has not installed?