There is no drain directly in the floor. You probably mean something like not having a shower tray and standing directly on the tile, then there would be a strainer and the drain underneath?
Regards
No, I don't mean a drain in the shower, but in the floor somewhere else in the room. It's quite useful, for example, if the washing machine (in case there is one in the bathroom) bursts. In our rental apartment, there is such a drain and I have to pour water into it every few weeks, otherwise there is no trap water left in it.
Do you have a ventilation system? Acquaintances initially had the same problem until it was discovered that the [Kontrollierte-Wohnraumlüftung] was wired incorrectly. Both fans were extracting air, creating negative pressure in the house, and the air was being drawn in through the drainage vent pipes.
- extractor hood in the kitchen with filter (air does not go outside)
- chimney is present / fireplace not yet connected
- boiler is located in the utility room