Building acceptance of new construction despite missing heat pump. Significant defects?

Unfortunately, nothing about the consequences of non-fulfillment is stated in the purchase contract.

Informal, immediate, fruitless. Delivery and service contracts without penalties are basically more like memorandums.

In that case, he would have either cut himself on me or traded with lemons. I would gratefully acknowledge receipt of his notification regarding the circumstance and its consequence of the invalidity of the acceptance date, and set him a deadline of 14 days after receipt to
1. requalify his message concerning the execution and duration of the provisional solution;
2. declare his choice whether he now wishes to initially carry out a partial acceptance;
3. make a binding statement about which extension period he requests; and
4. submit two proposals for a mutually agreed-upon date for the partial or final acceptance.

First of all, thank you very much for your detailed feedback.

So I should refuse the acceptance in writing and justify it with the missing heat pump and at the same time demand that he specifically respond to the points you mentioned within the 14-day deadline?

Exactly: where are you in the payment plan, which retention are we talking about, and which penalties have been agreed?

Most recently (in July), we made payment of installment E) according to the developer and brokerage contract amounting to 12.6% of the purchase price for the following work:
"After completion of the rough installation of the heating system, the electrical systems, ...".
Now the developer is simultaneously demanding payment of installment F) with the letter regarding the acceptance date. Without this, acceptance would not be carried out. Installment F) is due:
"after completion of the tiling work in the sanitary area and the façade work and after readiness for occupancy and simultaneously against handover of possession with 13.3%."

Oral statements from which source?
Currently, you actually hear a lot everywhere about delivery delays of heat pumps. In this respect, I tend to the assumption "in dubio pro reo" that there is indeed a genuine delivery bottleneck here. If you know the supplier, however, an inquiry whether this is actually the reason cannot hurt. If necessary, also talk to your lawyer as to whether he would consider you "authorized to apply on behalf of others" to have the solvency of the company judicially examined if needed.

The oral statement came from the developer.

Readiness for occupancy is not given without heating.

Readiness for occupancy is not given without heating.

Thanks also for your feedback (and of course to the others as well).

In my opinion, too. However, he writes that he will help us out here with temporary solutions without specifically stating what kind of temporary solution he will provide us.

...and how he wants to encourage you to accept the provisos (money, gold, compulsory labor). If he, for example, came with a fan heater, I would sue him for bodily injury because I wouldn't be able to stop laughing for years.

I would still appreciate further feedback. I have to honestly tell you that I am still unsure about how to best proceed now. I actually want to avoid hiring a lawyer, as I do not have legal insurance and need the money - for reasons given - for other things. However, I fear that engaging a lawyer is unavoidable.