Air heat pump or use gas and solar?

I have serious concerns about the maintenance costs; therefore, I view it critically.

I have major concerns about the maintenance costs; therefore, I view this critically.

Ground source heat pumps do not have higher maintenance costs than other heat pumps.

Sole heat pump does not have more maintenance costs than other heat pumps.

That may be true. Nevertheless, the nearly 400 euros per year according to the Waterkotte website is too steep for me.

What do they do for 400€? You don't have to let yourself be talked into every crap.

Brine heat pumps do not have higher maintenance costs than other heat pumps.

A brine heat pump - unless it is operated with well water - is a reliable, long-lasting, and above all maintenance-free solution.
If electricity prices explode, you can at least counteract that directly with the photovoltaic system....

An air heat pump, on the other hand, has more moving parts, is located outdoors.... and a few things need to be considered structurally (condensate drainage, decoupling, electrical supply lines, noise issues?)

With gas and oil heating systems, I increasingly get the impression that people want the cheapest "box" possible, the heating engineer sells the cheapest part, and then the problems begin. Quality is no longer valued here.

Two of my colleagues each have Viessmann and a no-name brand in their new builds (about 5 years old).
What has already been replaced during the warranty period and even after... The heating engineer comes and comes, the manufacturer technician comes and comes...
I don't know all manufacturers for oil/gas, but in my family, Weishaupt oil condensing boilers are used exclusively - without problems. The oldest oil boiler (without condensing technology) has been running without issues for over 25 years...

But basically, difficult topic
... Whether it was the right decision, unfortunately, you only know after years....

This is the maintenance contract. You have to do it if you want to keep the warranty, which certainly makes sense for a new device.

I find that unprofessional and therefore I also reject such a product.