Inside a standard toilet tank, there are three important parts: the flapper, the fill valve and the flush valve. The flapper is the rubber piece attached to the flush lever chain. It lifts up and down to make the toilet flush. Older fill valves often have a floating oval-shaped ball attached to a horizontal rod; newer valves have a simple cylinder-shaped float. Both slide up and down as the water level in the tank rises or falls. The flush valve is made up of the seat for the flapper and the overflow tube. If a toilet is running constantly, it is probably time to replace the flapper. If that does not solve the problem, the fill valve most likely needs to be replaced.
Step 1: Use the shutoff valve located below the toilet to turn off the water supply to the tank. Flush the toilet and use a sponge to soak up the remaining water in the tank. Place some towels on the floor below the tank to catch any residual water that may leak out during the repair process.
Step 2: Remove the old fill valve by unscrewing the water supply line from the underside of the tank. Next, use an adjustable wrench to loosen and remove the nut located beneath the tank. Inside the tank, disconnect the fill tube from the overflow pipe and lift out the old fill valve.
Step 3: Use the water line marks inside the tank as a guide for adjusting the new fill valve to the appropriate height. Make sure the fill valve does not touch the sides or top of the toilet tank. Reference the fill valve instructions for other necessary adjustments before completing the installation.
Step 4: Place the shank washer on the fill valve shaft, insert the fill valve through the base of the tank and hand-tighten the lock nut beneath the tank. Tightening the nut too much could crack the porcelain, resulting in the need for a whole new toilet, so be careful.
Step 5: Once the new fill valve is in position and functional, reconnect the water supply line and attach the fill tube from the fill valve to the overflow pipe. Follow the fill valve instructions to make any additional adjustments, turn the water supply back on, check for leaks, and flush away at will.