New Japan resident- trouble setting up hot water heater

hello everyone, I took procession of my apartment today and is trying to set up my electric hot water heater.

From i can gathered from the manual, the step is as follow

1) open the pressure valve, water valve and the water output valve (output to your unit), to allow the water to start filling the tank.

2) once the tank is full, close the pressure valve and turn on the power.

3) set the water temperature setting / power setting using the panel.

the problem i am having is I dont think the water tank is filling up, I can hear the water flowing, but after 3 hour, it is still going and would stop if close the pressure valve.

does anyone know what I am doing wrong?

thanks!!

by ADustInTheWind