If you’ve already replaced the flapper but your toilet is still running, the fill valve is likely the problem. Replacing it sounds intimidating but takes about 20 minutes and costs under $15.
What is a Fill Valve?
The fill valve controls the water that refills your tank after every flush. When it wears out it either runs constantly or makes a hissing noise. Both mean it needs replacing.
What You’ll Need
A replacement fill valve kit, an adjustable wrench, a sponge, and a bucket.
Step 1: Turn Off the Water
Turn the shut-off valve behind the toilet clockwise until the water stops. Flush the toilet to empty the tank. Use a sponge to soak up any remaining water.
Step 2: Disconnect the Water Supply Line
Unscrew the water supply line from the bottom of the tank by hand or with a wrench. Have a bucket ready — some water will drip out.
Step 3: Remove the Old Fill Valve
Inside the tank, unscrew the locknut on the bottom of the fill valve counterclockwise. Lift the old fill valve straight out.
Step 4: Install the New Fill Valve
Insert the new fill valve into the hole. Adjust the height according to your tank size — most kits have instructions. Hand tighten the locknut from underneath, then give it a quarter turn with a wrench.
Step 5: Reconnect and Adjust
Reconnect the water supply line. Turn the water back on slowly. Let the tank fill and check for leaks. Adjust the water level by turning the adjustment screw on top of the valve.
Recommended Fill Valve
The Fluidmaster 400A is the most popular fill valve in the world — used by plumbers and homeowners alike. It fits almost every toilet and costs around $12-30.