There is hot water below the fourth floor of the hotel, but the rooms above the fourth floor are normal, with hot water and cold water. What happened?

This is relatively simple. Most radiators are installed from the boiler room on the first floor to the highest floor (here, the fourth floor). Then the hot water is evenly distributed to each room, and the pipe is connected with a set of radiators from top to bottom, and you're done.

Because the hotel can provide hot water 24 hours a day, there is enough hot water for us to use.