Fix a toilet that runs

Steps

Goal: Open the tank, identify the cause, and fix the most common culprits in order.

• Lift the tank lid straight up with both hands and set it on a folded towel on the floor to prevent cracking. If the lid is stuck, wiggle it gently side to side while lifting. You should see the flapper, fill valve, float, and overflow tube inside the tank.
• Check the water level—it should sit about one inch below the top of the overflow tube. If water is actively flowing into the tube, the float is set too high. Watch for ripples at the top of the tube.
• Press down on the flapper with your finger. If the running stops, the flapper is not sealing. Lift the flapper and check for cracks, warping, or mineral buildup on the rubber and the flush valve seat. Verify the chain has about half an inch of slack.
• Good: You identified the cause—proceed to Fix the flapper or Adjust the float as needed.
• Bad: Unclear—work through Fix the flapper, Adjust the float, and Inspect the fill valve in order.

Fix the flapper

Goal: Replace a worn or warped flapper so it seals against the flush valve seat.

• Unhook the old flapper from the pegs on the overflow tube and disconnect the chain from the flush lever.
• If the flush valve seat feels rough, wipe it with a cloth and fine-grit sandpaper to smooth it before installing the new flapper.
• Install the new flapper and reconnect the chain with about half an inch of slack. Press the flapper down—it should sit flat and stay in place without assistance.
• Good: The flapper seals; running stops when you press it down. Proceed to Test the repair.
• Bad: Still runs—check the float level (see Adjust the float) or the fill valve (see Inspect the fill valve).

Adjust the float

Goal: Set the water level about one inch below the overflow tube so water does not spill over.

• Turn the adjustment screw on a ball-cock float arm clockwise to lower the float, or slide the clip down on a cylinder-style float.
• If the float is cracked or waterlogged, replace it—adjusting a damaged float will not hold.
• Flush and watch the tank refill. The water should stop filling approximately one inch below the overflow tube rim.
• Good: Water stops at the correct level; no spill into the overflow tube. Proceed to Test the repair.
• Bad: Still overflows or the fill valve does not shut off—see Inspect the fill valve.

Inspect the fill valve

Goal: Confirm the fill valve shuts off cleanly when the tank is full.

• Flush the toilet and watch the fill valve as the tank refills. It should shut off cleanly once the water reaches the float level.
• If the valve dribbles or does not shut off, twist the top cap counterclockwise to remove it and rinse debris from the seal. Reassemble and flush again.
• Good: The valve shuts off crisply; no dribbling. Proceed to Test the repair.
• Bad: Valve still dribbles or will not shut off—replace the fill valve assembly or call a plumber.

Check overflow tube

Goal: Confirm the overflow tube is intact and tall enough that normal fill levels never reach its rim.

• Check that the overflow tube is intact and water stays below its rim. The tube should be tall enough that the water level stays below its top.
• If the tube is cracked or too short, call a plumber—replacing it usually requires removing the tank.
• During a normal fill cycle, confirm no water trickles into the tube. You should see the water level hold below the tube rim.

Test the repair

Goal: Confirm the toilet is fixed and stays silent after flushing.

• Flush the toilet two or three times. Wait at least sixty seconds after each flush. Listen for any running water, trickling, or hissing.
• Good: The tank stabilizes and you hear complete silence within a minute of each flush. The repair is complete.
• Bad: Still runs—recheck the flapper seal and float height. If you have replaced the flapper and adjusted the float and the toilet still runs, see When to get help.

When to get help

If water is overflowing, shut off the main water supply first.

Call a plumber if:

• You have replaced the flapper and adjusted the float but the toilet still runs.
• You see water leaking outside the tank (on the floor or at the base).
• The flush valve seat is cracked or pitted beyond light sanding.
• The tank is cracked.

For other plumbing fixes, see How to shut off the main water supply, Fix a leaking faucet, or How to unclog a drain.

Verification

• The toilet is completely silent sixty seconds after a flush—no trickling or hissing.
• The water level in the tank stabilizes about one inch below the overflow tube.
• No water movement in the bowl: place a few drops of food coloring in the tank and wait fifteen minutes—the bowl water should stay clear.