How to Install a New Toilet Fill Valve

Replacing a toilet fill valve—also called a ballcock or inlet valve—is one of the most common and rewarding bathroom repairs. The fill valve is what refills your tank after you flush, and when it wears out, you'll hear constant hissing, see water trickling into the bowl, or watch the tank never quite fill right. A bad fill valve doesn't get better on its own; it only gets noisier and wastes water. The good news is that modern fill valves are cheap, durable, and straightforward to swap. You don't need a plumber. The job is mechanical, not tricky, and once you understand the three main connections—the water line, the tank opening, and the overflow tube—you're essentially done. Most people finish this in forty-five minutes.

1. Shut Off Water First. Locate the shutoff valve on the water line below the toilet, usually on the left side near the floor. Turn it clockwise until it stops. Then flush the toilet and hold the handle down to drain as much water from the tank as possible. If water remains in the bowl, use a cup or sponge to remove it—you want the tank as dry as you can get it.
2. Disconnect Supply Line. Look under the tank where the water line enters. You'll see a compression nut connecting the flexible supply tube to the base of the fill valve. Use an adjustable wrench to hold the fitting on the valve itself while you turn the nut counterclockwise with a second wrench. Once it's loose enough, unscrew it by hand. Pull the supply line away and set it aside. Water may drip, so have a towel ready.
3. Detach Overflow Tube. Inside the tank, you'll see a hollow plastic or metal tube that runs down the center. This is the overflow tube. The fill valve inlet sits inside or near this tube. Look for where the fill valve connects to the overflow tube—there's usually a small clip or the tube simply slides over the valve outlet. Gently slide the tube off the outlet or release the clip. You don't have to remove the overflow tube from the tank; just disconnect it from the fill valve.
4. Loosen Locknut Below Tank. Under the tank, you'll see a large nut threaded onto the fill valve stem. This is the locknut. Use an adjustable wrench or a dedicated locknut wrench to turn it counterclockwise. It will loosen gradually. Once it's loose enough to turn by hand, unscrew it completely. The fill valve will now be free to lift out of the tank from above.
5. Extract Old Valve. From inside the tank, grip the top of the old fill valve and pull it straight up and out. It will slide through the tank opening. Set it aside. Look at the opening where it came from—you may see a rubber or plastic washer that seals the hole. If it's cracked, deteriorated, or stuck, remove it now. Wipe the opening clean with a dry cloth.
6. Insert New Valve. Examine the new fill valve. Most modern ones have a flat side that should face the back wall of the tank and the float arm extends toward the front. Read the manufacturer's instructions on the box—they're usually clear. Insert the valve through the tank opening from inside, orienting it as specified. Push it down until the threaded stem extends below the tank bottom by about half an inch. The valve should sit flush against the tank floor.
7. Secure With Locknut. From under the tank, thread the locknut onto the valve stem by hand first. This prevents cross-threading. Once it's hand-tight, use your adjustable wrench or locknut wrench to turn it clockwise. Tighten it firmly but not aggressively—you want a watertight seal without cracking the porcelain. It should feel snug and require modest force to turn.
8. Reattach Overflow Tube. From inside the tank, position the overflow tube so its opening slides over the small outlet on the new fill valve. Push it on gently until it seats. If your valve came with a clip, secure the tube with it. Make sure the tube sits vertically and straight; a bent or kinked overflow tube will cause the tank to drain slowly or not fill completely.
9. Reconnect Supply Line. Position the water supply line so it connects smoothly to the fill valve inlet without kinks. Thread the compression nut onto the fitting by hand first, then use two wrenches—one to hold the valve fitting steady, one to tighten the nut—and turn clockwise. Tighten until snug; hand-tighten first, then another quarter-turn with the wrench.
10. Power On and Listen. Turn the shutoff valve counterclockwise slowly. Water will begin flowing into the tank. Watch the fill valve work—you should hear water flowing in, and you should see the float arm rise as the tank fills. Once full, the fill valve should stop the water flow. Flush the toilet and listen to it refill. The sound should be smooth and quiet without hissing or chattering.
11. Inspect For Leaks. Get under or behind the toilet with a dry cloth and inspect all three connection points: the water supply line nut, the locknut around the valve stem, and anywhere the overflow tube connects inside the tank. If you see drips or water pooling, tighten the relevant fitting a quarter-turn and wait a minute. Check again. Most leaks stop immediately once tightened properly.
12. Tune Float Height. Modern fill valves have a float adjustment mechanism—usually a small clip or screw on the float arm. If the tank is overflowing into the overflow tube or not filling high enough, gently adjust the float. Consult the instructions on your valve box for the specific method. Small adjustments go a long way; move the float up a quarter-inch if you need more water, down a quarter-inch if you need less.