Replace Fill Valve

If adjusting the float doesn't work or if the fill valve itself is leaking or malfunctioning (e.g., not shutting off water completely), the entire fill valve assembly may need replacement. Turn off the water supply valve behind the toilet. Flush the toilet to empty the tank. Use a sponge to remove remaining water. Disconnect the water supply line from the bottom of the tank. Unscrew the locknut holding the fill valve in place and remove the old valve. Install the new fill valve according to manufacturer instructions, reconnect the supply line, and turn the water back on, checking for leaks and proper water level.