Novice here. The fill valve was leaking and causing the water to coming very very slow. Like 45 minutes to fill up tank. I bought a fill valve top and replaced it. Let me add that I did turn water off at the supply valve but water was still trickling up the fill valve. Like the water was not completely shutting off.
After replacement I turned the water back on and the water would not stop coming in the tank. Even when the float lifted on the fill valve. I flushed and same thing. Turned water off again and water would very slowly start filling the tank.
EDIT: From comments I will have to replace the Fill Valve. My concern is the supply valve not completely shutting the water off. This is a older house so it would have to be shut off at the main. I don't know how to do this.
If there is very little water coming out from the supply valve could I still install/hook up the Fill Valve?