How do I get out of a contract for work?

I have mentioned it several times already: unfortunately, we are having massive problems with our glazier, who is supposed to do the gallery and stair railing for us.

The first installation was at the beginning of July last year. All the glass panes were defective or cut incorrectly. Then nothing happened for a long time until I set a deadline for rectification by email. Then finally there was communication again. One replaced pane in the first rectification was cut incorrectly again (so we are now supposedly receiving the third version—if it ever arrives). The four glasses of the gallery railing are all defective and are to be replaced (they are all covered with lime streaks).
Supposedly, the supplier delivered faulty panes to the glazier again, which the glazier then initially did not bring because they were defective (if what he says is true—we don’t actually know).

By now, we have been waiting for half a year for our gallery and stairs to finally receive the final railing. We are getting quite annoyed and would like to terminate the contract. So, in short: he should pack up his stuff, and we will realize this with another company.

I know that with a normal contract for work (I assume that’s what we have—we only once received an offer a long time ago and accepted it verbally), it’s not so easy to get out of it again. But also not impossible. After 6 months, we believe that enough time was given to make the necessary corrections. That the glazier only receives faulty goods from his supplier is not our problem; we have the contract with the glazier.

As I said: a written request with a deadline has already been sent; what else do I need to do in order to be in a legal position to terminate this contract? Is that even possible?

How about the 648a - termination without notice for good cause, as it is unreasonable for you to wait any longer for a defect-free result. Alternatively, and at the same time, an ordinary termination due to non-fulfillment.

Has any money been transferred yet?

No, thank God not yet

Briefly summarized:

- Set a deadline for supplementary performance (§323 para. 1 Baugesetzbuch) >>> if this is missed, secondary warranty claims under contract law apply >>> including your intended withdrawal pursuant to § 634 no. 3 in conjunction with §§ 636 and 323 Baugesetzbuch.

Edit: Termination for good cause pursuant to §648a Baugesetzbuch exists in parallel as already written by nordanney - unfortunately the legislator failed to specify the "good cause" here Furthermore, the termination only applies to services not yet rendered >>> for existing defects one reverts to the withdrawal section.

Contrary to my usual habit, I would set aside emotion and answer a few questions before trying to get out of the work contract: 1. What is the likelihood that another glazier will work better, faster, and at similar costs? I would research the answers in advance. 2. What is the likelihood that my glazier can or wants to still do the railing well? Here I would simply ask him openly. Perhaps he no longer wants the contract because it causes him more trouble than he wants. Then ending the contract with a mutual declaration of intent would not be a problem. No costs, no harsh words, and done. 3. What could be important reasons for terminating the contract? Is an acceptance pending, are other trades hindered by the absence of the railing, are there hazards... 4. What cost risks can I expect if I cancel the contract? Research in advance or read the contract.