The vacuum cleaner has a level switch. If there is little water in the pool / well (min. approx. 30 cm), the pump does not switch on. The product is not usable.
Mfg Sarjanartus

I also had this problem. I then removed the white fine filter. Immersed the unit in the pool and turned on the switch and it worked again. It is important that when the fine filter is over the black filter, the housing can be screwed together easily and without much pressure.