Its obvious the float ball has punctured and there is water inside.

Dude. Your plumber fcuked up the water inlet and outlet already. 2 pictures already exposed the problem. One of it is this,



If you link the inlet and outlet, once the tank fills up and stops, the additional pressure will go to the second outler pipe. Assuming second pipe also stops due to normal faucet on/off, the water pressure has to go somewhere, it goes back to tank la. hahaha.