How to Fix a Running Toilet

A running toilet is usually caused by a flapper that won't seal, a chain that's too long or short, or a water level that's set incorrectly. Most fixes take under 30 minutes with basic adjustments.

1. Open the Tank Safely. Carefully lift the ceramic lid straight up and set it aside on a towel or soft surface. The lid is heavy and can crack easily, so handle it with both hands and avoid placing it on hard surfaces.
2. Diagnose the Culprit. Look at the rubber flapper at the bottom of the tank. Press it down firmly against the flush valve seat. If water stops running, the flapper isn't sealing properly. Clean any debris from around the seat and check if the flapper is warped or cracked.
3. Fine-Tune the Chain. The chain connecting the flush handle to the flapper should have about half an inch of slack when the flapper is closed. If it's too tight, the flapper can't close completely. If it's too loose, the flapper won't lift when you flush. Adjust the chain length by moving the clip to a different link.
4. Lower the Waterline. The water should sit about one inch below the rim of the overflow tube. If it's higher, water spills into the overflow tube constantly. Bend the float arm down gently to lower the water level, or adjust the screw on newer float cup mechanisms.
5. Swap Out the Flapper. If the flapper is warped, cracked, or won't seal after cleaning, unhook the chain and lift the flapper off its hinges. Take it to the hardware store to match the size and shape exactly. Install the new flapper by reversing the removal process.
6. Verify the Fix Works. Replace the tank lid and flush several times. Listen for the fill cycle to stop completely within a minute or two. If water continues running, repeat the adjustment process, focusing on the component that seemed most problematic.