How to fix a running toilet

Steps

Goal: Identify why the toilet runs and fix the flapper, fill valve, or float.

• Remove the tank lid. Flush and watch the fill cycle. Note whether water runs continuously.
• Good: You can see the flapper and fill valve. Proceed to Check the flapper.
• Bad: Water runs from somewhere else—see When to get help.

Check the flapper

Goal: Confirm the flapper seals properly.

• Look at the flapper. It should sit flat over the drain. Press it down—does the running stop?
• Inspect for cracks, tears, or mineral buildup. Replace if worn.
• Good: Flapper seals and running stops. Proceed to Verification.
• Bad: Flapper is worn or does not seal—replace it. Proceed to Replace the flapper.

Adjust the float

Goal: Set the water level to about 1 inch below the top of the overflow tube.

• If water overflows into the tube, lower the float. On a ball float, bend the arm down. On a fill valve, turn the adjustment screw or slide the clip.
• Flush and verify the water stops at the correct level.
• Good: Water stops at the fill line. Proceed to Verification.
• Bad: Still overflows—check the fill valve or replace it.

Replace the flapper

Goal: Install a new flapper when the old one is worn.

• Turn off the water supply. Flush to empty the tank. Unhook the old flapper.
• Install the new flapper—match size and shape. Reattach the chain with minimal slack.
• Turn the water back on. Flush and test.
• Good: Flapper closes fully; running stops. Proceed to Verification.
• Bad: Still runs—check the fill tube and fill valve.

When to get help

Call a plumber if:

• The tank leaks at the base (could be a broken tank or bad gasket).
• You hear water running when no fixture is used (possible main-line leak).
• The fill valve or flapper replacement does not stop the running.

Verification

• Flush the toilet. After the tank refills, listen for 30 seconds—no running.
• Add food coloring to the tank. Wait 5 minutes—no color in the bowl.
• Water level stays at the fill line (about 1 inch below the overflow tube).