Main lines incorrectly installed

You certainly don't want your boss to criticize and reprimand your work before the file is closed, the customer is contacted, or the product moves to the next line.

So far, the damage is in the upper four-figure range and can be repaired.

You certainly don’t want your boss to criticize and reprimand your work before the file is closed, the customer is contacted, or the product moves to the next stage.

I don’t want to disagree with you that one should initially try it in a friendly/verbal way. But the example is poorly chosen: Of course I want to be pointed out a mistake before the product goes to the customer.

By the way, we recently had a (small) defect in the heating system; one year after moving in. So I politely wrote an email* to the installer. Nothing happened. Tried again. Nothing happened. New email with a rather neutral text to the developer with the installer in cc. Bam: appointment for repair arranged. And when you’ve had experiences like this more often, next time you just immediately resort to the effective measure.

*Yes, the phone might be even friendlier, but I typically only have time for "such things" outside regular business hours.

*Yes, the phone might be friendlier, but I typically only have time for "such things" outside of regular business hours.

The phone is not evidence in case of defects. I had also pointed it out by phone. The response was that 10 cm is always doable. Now unfortunately it is 100 cm. So I chose the written form.

Phone calls are not proof of defects. I have also pointed it out by phone before. The response was that 10 cm is always feasible. Now, unfortunately, it is 100 cm. Therefore, I chose the written form.

and that is also correct with email.

Email is perfectly fine for normal communication. If you want to put the other party in default, you must be able to prove receipt, so practically only a registered letter with proof of delivery is an option. However, then you are no longer on the level where adults normally talk to each other.

But then you are no longer at the level where adults talk to each other normally.

Well, being just kind, nice, and empathetic, the reprimand can unfortunately lack the legally required form. And then the next trade comes along and continues in good faith based on proper preceding work, and then you end up with the mess, sauce and all.