Fix a Running Toilet

Running toilets are one of those problems that seem minor until you realize it's costing you money and wasting water every single day. The tank refills constantly, sometimes barely audibly, sometimes with a noticeable hiss. Left unfixed, a running toilet wastes thousands of gallons a year and drives your water bill up month after month. The good news: the fix is almost never complicated. The toilet tank has only a few moving parts, and when one wears out, the whole system falls apart. You're looking at a straightforward repair that takes basic tools and no special knowledge—just the ability to turn off water, remove a few bolts, and swap out the faulty piece. Done right, your toilet will be silent and your water bill will drop.

1. Shut Off the Water First. Locate the water shutoff valve behind or beneath the toilet, usually on the left side of the bowl. Turn it clockwise until it stops. Flush the toilet to empty the tank. If water keeps trickling out, turn the valve a bit more—you may need to turn it a full two or three rotations to seat it properly.
2. Find the Trickling Culprit. Look inside the tank at the left side (or right, depending on the toilet model). You'll see a tall cylinder connected to the water supply line—this is the fill valve. Watch the water level. If the tank is full and water is still trickling into it, the fill valve seat is worn and needs replacement. If water is instead leaking out through the overflow tube in the center of the tank, move to the flapper check.
3. Check Seal Integrity. The flapper is a rubber seal at the bottom of the tank that opens when you flush and closes to stop water flowing into the bowl. Look at the overflow tube—if water is pouring down it even when the tank is full, the flapper isn't sealing. You can also gently press down on the flapper with your finger (tank is now empty) to see if it rocks back and forth loosely or if it's warped.
4. Unscrew the Old Valve. Position a bucket under the water supply connection at the base of the fill valve. Use an adjustable wrench to disconnect the supply line. From inside the tank, use a large slip wrench or adjustable wrench to grip the fill valve's base nut (underneath the tank, accessible from below). Turn counterclockwise to unscrew it. The valve will pull up and out of the tank. Some water will drain—the bucket catches this.
5. Wipe the Mounting Hole Clean. Before you install a new fill valve, clean out the valve seat—the hole where the old valve sat. Use a wet cloth to wipe away any mineral deposits or debris. Look inside with a flashlight; the seat should be smooth and relatively clean. If it's pitted or heavily stained with mineral buildup, you can use a fine-grit sandpaper or a plastic brush, but don't gouge it.
6. Seat the New Valve Snugly. Set the new fill valve into the hole and thread the base nut by hand first to avoid cross-threading. Once hand-tight, use your wrench to tighten the nut snugly but not aggressively—you're aiming for firm, not crushed. Reconnect the water supply line and tighten it by hand, then give it a quarter turn with the wrench. Turn the shutoff valve back on slowly and listen for leaks.
7. Install the New Flapper. With the tank empty and water off, locate the flapper at the bottom center of the tank. It's held in place by ears or slots that fit onto a shaft running across the tank. Lift the old flapper up and off. Clean the valve seat with a damp cloth to remove any grit or mineral deposits. Set the new flapper onto the shaft, making sure the ears sit evenly on both sides. The flapper should move freely up and down without binding.
8. Listen for Silence. Turn the water shutoff valve back on slowly. Watch the tank fill completely. Once full, water should stop flowing in completely—no trickling, no hissing. Listen for at least 30 seconds of silence. Flush the toilet and watch it refill. The flapper should snap shut immediately, and the fill valve should cut off when the tank reaches its mark. If everything is silent and the bowl drains normally, you're done.
9. Inspect for Hidden Drips. Lie on your back with a towel or lay down beside the toilet to look at the underside of the tank, particularly around the fill valve connection and supply line. Leave the water running for a few minutes and check for drips. Any leak at the nut connection means you need to tighten it more; use the wrench for a quarter turn and check again.
10. Dial In the Water Level. If the tank fills higher or lower than before, or if you notice water is barely trickling into the bowl, you may need to adjust the fill valve's level setting. On most valves, this is a small clip or screw on the side of the valve body that you can adjust while the water is on. Make small adjustments—one quarter turn at a time—and wait for the tank to refill between adjustments.
11. Watch Overnight for Silence. Don't assume the job is finished immediately. Let the toilet sit unused for several hours or overnight. Check in the morning to make sure the tank is still full and hasn't refilled overnight. Also flush several times throughout the day to ensure consistent refill behavior. A toilet that runs only after many flushes may have a flapper that's still breaking in or a fill valve that needs a slight adjustment.