How to Replace a Leaking Toilet Fill Valve

A leaking toilet fill valve—also called a ballcock or inlet valve—is one of those failures that starts small and gets expensive fast. That constant trickle into the bowl wastes water, runs up your bill, and wears out other tank components. The good news is that replacing it is one of the most straightforward plumbing jobs a homeowner can do. You don't need special skills or tools, and you'll save yourself the cost of a service call. This guide walks you through the exact steps to get your toilet working quietly and efficiently again.

1. Locate and close the shutoff valve. Locate the shutoff valve on the water line running to the toilet tank. It's usually on the wall or floor behind the toilet. Turn the handle clockwise until it stops. Flush the toilet to confirm the water is off and the tank is emptying normally. If you can't find the shutoff valve or it doesn't work, you'll need to shut off the main water supply to the house.
2. Empty the tank completely. Flush the toilet to clear the water from the tank. If the fill valve is leaking badly, the tank may not refill completely, which is fine. Use a sponge or small cup to remove any remaining water from the bottom of the tank. This keeps water from spilling onto your floor during removal.
3. Disconnect the supply line. Use an adjustable wrench to loosen the compression nut connecting the water supply line to the base of the fill valve. Turn counterclockwise until the nut is loose enough to unscrew by hand. Keep a small bucket or towel underneath to catch any remaining water in the line. Once the nut is free, pull the supply line away from the valve.
4. Unscrew the lock nut. Reach under the tank from the outside. You'll see the fill valve extending through the bottom, with a large lock nut holding it in place. Use an adjustable wrench or fill-valve socket wrench to grip the lock nut and turn it counterclockwise. You may need to hold the fill valve stem steady with your other hand so it doesn't spin. Turn until the nut comes completely free and you can lift it away.
5. Extract the old valve. From inside the tank, grab the fill valve stem and pull it straight up and out. It should come free without resistance. You may need to wiggle it slightly if it's tight. Once out, inspect the hole in the tank bottom. It should be clean and free of mineral deposits. If there's buildup, wipe it out with a damp cloth.
6. Clean the tank opening. Clean the underside of the tank around the fill valve opening. Remove any old rubber washer pieces, mineral deposits, or corrosion with a cloth or old toothbrush. A clean, smooth surface ensures a watertight seal with your new valve. Pay special attention to the inside edge of the opening where the new rubber washer will sit.
7. Position the rubber washer. Most new fill valves come with a rubber washer and lock nut included. Slide the rubber washer onto the fill valve stem from the bottom, pushing it up until it sits flush against the base of the valve body. This washer is what creates the watertight seal, so it must be positioned correctly. Some newer valves have a built-in washer—check your instructions.
8. Seat the new valve. From inside the tank, position the new fill valve stem through the tank opening. Push it straight down and slightly toward the back of the tank, seating it fully. You should feel it drop into place. The rubber washer should be compressed against the tank bottom, creating a seal. The valve body should sit snugly against the underside of the tank.
9. Secure the lock nut. From below the tank, slide the lock nut onto the fill valve stem. Using an adjustable wrench or fill-valve wrench, tighten it clockwise. Turn hand-tight first, then give it another quarter turn with the wrench. Don't over-tighten—you'll crush the washer and create a different leak. The valve should be secure and not wiggle, but not cranked down hard.
10. Reattach the water line. Take the supply line you disconnected earlier and screw it back onto the fill valve's inlet port. Use your wrench to tighten the compression nut, turning clockwise. Again, hand-tight plus a quarter turn is the rule—you're not trying to crush it. Make sure the line is routed the same way it was before (use your tape mark as reference).
11. Restore water and verify fill. Slowly turn the shutoff valve counterclockwise to restore water to the tank. Watch and listen as the tank fills. The new fill valve should produce water and then shut off smoothly once the tank reaches full level. The fill action should be smooth and quiet—no hissing, hammering, or continued dripping after the tank is full. Flush once to confirm the cycle repeats correctly.
12. Confirm the seal is dry. Place a dry towel underneath the tank where the fill valve connects. Wait 10 minutes. If the towel stays dry, you're done. If you see moisture, the lock nut is leaking. Turn off the water, dry everything, and give the lock nut another quarter turn. Turn the water back on and check again. If the leak persists, turn off the water and reseat the rubber washer—it may have shifted.