Eventually I realized something was wrong with the water in my apartment.
There was low pressure, and the boiler was giving almost no hot water.
I contacted plumbers, but everyone gave different explanations — old system.
I searched for clear information. That’s how I found this website:
https://stroyka2001.kh.ua There they clearly explain common water-related problems.
After reading a few articles, I understood what had been overlooked.
I advise paying attention to it to anyone who wants to figure out water problems.