Maintenance contract residential ventilation, cheaper filters

Points to be maintained for a heat pump:

- Over time, a lot of dust and dirt accumulate on and inside the outdoor unit. This affects the compressor, which is necessary for the smooth operation of the heat pump. Monoblock units also have a compressor, and it must also be cleaned regularly.

- The ventilation slats should be clean. For outdoor units, a high-pressure cleaner can be used for cleaning. For indoor units, the slats must be cleaned by hand from dust and dirt.

- The most important point here is the leak test of the system. Refrigerant is usually highly environmentally hazardous. Since the fluid is in a closed circuit, refrigerant usually only leaks if there is a leak, e.g., due to poor installation or vibrations of the system. Loss of refrigerant can lead to the failure of the entire system.

- Replace or refill refrigerant (only if necessary). Eliminate leaks.

- As a final step, the technician must subject the overall functionality of the system to a test.

Thank you very much for the answers, very helpful for laypersons.

I agree with you regarding outdoor units. There might actually be something to maintain here. I have a brine heat pump, there is no outdoor unit. Does one need to specially check the system for tightness? Shouldn't all the parameters of the heat pump get so mixed up with missing refrigerant that the system shuts down or at least reports an error? I don't have the air conditioning in my car checked for refrigerant as long as it works. I doubt that a simple inspection can prevent the leakage of refrigerant. Either the refrigerant has already escaped or there is no leak.

On the topic of ventilation: I don't know the thread. A filter set from Zehnder costs about €20 more than a cheap replica. According to its own specifications, my ventilation system currently uses 20 watts (somewhat quite low). With €20, I can operate my ventilation system for 126 days. So if I had (let's say) 20% energy savings, it would only pay off after more than 600 days. Furthermore, there is the risk that people keep expensive filters in the system longer than cheap ones. Which I don't think makes sense.

Some people only buy original filters for their extractor hood or vacuum cleaner because they are afraid of breaking something otherwise. Others buy the recommended descaler for their coffee machine from a Swiss manufacturer for €14/100ml. On my Ford, it says on the fuel cap "We recommend Aral gasoline." It’s all a matter of belief.

If refrigerant is missing, shouldn't all parameters of the heat pump become so disturbed that the system shuts down or at least reports an error?

Eventually yes, however, leaks are usually gradual so that only the efficiency suffers. Until, of course, the critical point is undershot and the system refuses to operate.

I doubt that purely through inspection you can prevent the loss of refrigerant.

No, the refrigerant is already gone at that point, if there is a leak. But the inspection will prevent further environmental damage. The refrigerant is supposed to remain in the device and not escape into the environment. The rules and regulations are clearly defined (DIN EN 378-1).

I don’t have my car’s air conditioning checked for refrigerant as long as it works.

Exactly, until it stops working because... well, because refrigerant is gone (which might only happen after you have already sold the car). Ask a workshop how often this happens, you will be surprised. Just because you don’t do something doesn’t mean it doesn’t exist. A whole guild (refrigeration and air conditioning tradespeople, as they are called colloquially) of masters and technicians is not there for no reason.

Either the refrigerant has already escaped or there is no leak.

To prevent the refrigerant from eventually escaping (rubber parts become porous, metal fatigues, connections loosen due to vibrations etc.), there are maintenance intervals including leak tests, yes, also for heat pumps. Also here DIN EN 378.

Some people buy only the original filters for their range hood or vacuum cleaner because they are afraid of damaging something otherwise. Others buy the descaler recommended for their coffee machine from a Swiss manufacturer for €14/100ml. On my Ford, the fuel cap says "We recommend Aral gasoline." It's all a matter of belief.
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I found the mentioned post from :
https://www.hausbau-forum.de/threads/zehnder-q350-problem-diskussionsthread.41994/post-544533

You can decide for yourself whether it is purely a matter of belief.
I found it quite plausible and understandable in individual cases. Certainly not universally applicable and not for all filters, but that was not the point! Only that one should consider such possible "side effects" before being happy about saving over €20 on filter purchases....

I think I will not take out a maintenance contract nor buy the original filter mats, I found a good alternative. I won't run the ventilation over the summer anyway, since the windows are open. Many people in the house don't use the ventilation at all because of the noise. Since it is a new building and there isn't much ventilation in winter, I didn't want to get mold in the apartment. Thanks for your advice!