Fix a Running Toilet Fill Valve

Water trickling into the bowl after every flush isn't just annoying—it's expensive. A running toilet can waste 200 gallons per day, turning a $2 hardware fix into a $50 monthly leak on your water bill. The fill valve controls when fresh water enters the tank after a flush, and when it fails, the tank never quite fills or stops filling. Most running toilets trace back to either a worn flapper or a fill valve that won't shut off. The fill valve is the tall assembly on the left side of your tank with a tube running to the overflow pipe. Replacing it requires no special skills, just a willingness to get your hands briefly wet and thirty minutes of uninterrupted time. You'll shut off the water, drain the tank, swap the valve, and restore flow—straightforward mechanical work that eliminates the constant background hiss of wasted water.

1. Listen and Watch the Tank. Remove the tank lid and flush. Watch the water level as the tank refills. If water keeps running after the tank fills, or if it overflows into the center tube, the fill valve isn't shutting off. Jiggle the float arm gently—if the water stops, the valve mechanism is sticking. If jiggling does nothing and water continues flowing, replacement is the solution.
2. Shut Off and Drain. Locate the oval shutoff valve on the wall or floor behind the toilet, usually on the left side. Turn it clockwise until it stops—this cuts water to the tank. Flush the toilet once to drain most of the water. Use a sponge or old towel to soak up the remaining inch of water in the bottom of the tank until it's nearly dry.
3. Loosen the Supply Connection. Place a small bucket or towel under the supply line connection at the bottom of the tank. Use an adjustable wrench or pliers to loosen the coupling nut connecting the braided supply line to the base of the fill valve shank. Unthread it by hand once it's loose. Expect a small amount of water to drip out.
4. Extract the Old Valve. Inside the tank, unclip the refill tube from the overflow pipe. Reach under the tank and unscrew the plastic lock nut holding the fill valve shank in place—turn counterclockwise. Lift the entire fill valve assembly straight up and out of the tank. Check the rubber gasket on the shank; if it's cracked or compressed flat, the valve was already leaking.
5. Mount the New Valve. Adjust the height of the new valve so the top sits at least one inch above the overflow tube—most valves have a twist-lock height adjustment. Insert the valve shank through the tank hole from inside. Slide the rubber gasket onto the shank from underneath, then thread the lock nut on by hand and tighten snugly. The valve should stand straight and stable.
6. Reattach Supply and Refill Tube. Thread the supply line coupling nut onto the valve shank from beneath the tank. Tighten by hand, then give it a quarter turn with pliers—no more. Inside the tank, clip the small refill tube onto the overflow pipe so it angles down into the opening. This tube refills the bowl after each flush.
7. Fine-Tune Water Level. Turn the shutoff valve counterclockwise to restore water flow. Watch the tank fill. The water should stop about half an inch below the top of the overflow tube. If it's too high or low, adjust the float using the adjustment clip or screw on the side of the valve body. Most modern valves use a pinch clip you slide up or down.
8. Verify the Fix Works. Flush the toilet twice and watch the fill cycle. Water should stop flowing once the tank reaches the fill line. Check under the tank for drips at the supply line connection and around the lock nut. If you see moisture, tighten the connections slightly. Let the toilet sit for ten minutes, then check again—no running water sound means success.