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Fix a toilet that keeps running

We'll open the tank, identify the cause (flapper, float, or fill valve), and fix it so the toilet stops running.

Troubleshooting · Home plumbing
10–15 min
What you'll need
  • Replacement flapper (if needed; universal flappers fit most toilets)
  • Towel to protect the lid and catch drips
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Steps

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

  • Lift the tank lid and set it on a folded towel. 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 flowing into the tube, the float is set too high.
  • Press down on the flapper. If the running stops, the flapper is not sealing. Check for cracks, warping, or mineral buildup. 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.

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 and disconnect the chain. If the flush valve seat feels rough, smooth it with fine sandpaper.
  • Install the new flapper and reconnect the chain with about half an inch of slack. Confirm it sits flat on the seat.
  • Good: The flapper seals; running stops. Proceed to Test the repair.
  • Bad: Still runs—check the float (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.

  • 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. Flush and watch—the water should stop about one inch below the overflow tube rim.
  • Good: Water stops at the correct level. Proceed to Test the repair.
  • Bad: Still overflows—see Inspect the fill valve.

Inspect the fill valve

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

  • Flush 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 off and rinse debris from the seal. Reassemble and flush again.
  • Good: The valve shuts off crisply. Proceed to Test the repair.
  • Bad: Valve still dribbles—replace the fill valve assembly or call a plumber.

Test the repair

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

  • Flush two or three times. Wait at least sixty seconds after each flush. Listen for running water.
  • Good: The tank stabilizes and you hear complete silence. The repair is complete.
  • Bad: Still runs—recheck the flapper and float, or see When to get help.

When to get help

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.
  • The flush valve seat is cracked or pitted beyond light sanding.
  • The tank is cracked.

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 when the tank is full.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm symptom Verify the toilet runs after the tank fills.
  2. Flapper Replace or adjust the flapper so it seals.
  3. Float and fill valve Adjust the float; inspect the fill valve.
  4. Call a plumber Flush valve seat cracked, tank cracked, or repeated failures—call a plumber.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Whether pressing the flapper stops the running
  • Water level relative to overflow tube
  • Flapper and chain condition
  • Steps already tried

Is water spilling into the overflow tube?

The water level should sit about one inch below the top of the overflow tube. If water flows into the tube, the float is set too high.

Lift the tank lid. Check the water level—it should sit about one inch below the top of the overflow tube. Watch for ripples or water flowing into the tube. Good: you see the level. Bad: water spilling into tube = float too high.

Yes No

You can change your answer later.

Adjust the float

Lower the float so water stops about one inch below the overflow tube rim.

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. Flush and watch—water should stop about one inch below the tube rim. Good: water stops at correct level. Bad: still overflows—check fill valve.

Done

Does pressing the flapper stop the running?

If pressing down on the flapper stops the running, the flapper is not sealing properly.

Press down on the flapper with your finger. If the running stops, the flapper is not sealing. Lift it and check for cracks, warping, or mineral buildup. Verify the chain has about half an inch of slack. Good: you know if flapper is the cause. Bad: unclear—check chain and seat.

Yes No

You can change your answer later.

Replace the flapper

Unhook the old flapper from the pegs and disconnect the chain. If the flush valve seat feels rough, smooth it with fine sandpaper. Install the new flapper and reconnect the chain with half an inch of slack. Good: running stops. Bad: still runs—adjust float or check fill valve.

Done

Does the fill valve shut off cleanly?

The fill valve should shut off once the water reaches the float level.

Flush and watch the fill valve as the tank refills. It should shut off cleanly. If it dribbles or does not shut off, twist the top cap off and rinse debris from the seal. Good: valve shuts off. Bad: still dribbles—replace fill valve or call a plumber.

Yes No

You can change your answer later.

Is the overflow tube cracked or too short?

A cracked or short tube needs a plumber.

Check the overflow tube. It should be tall enough that the water level stays below its rim. If cracked or too short, call a plumber. Good: tube is fine—test the repair. Bad: tube is damaged—call a plumber.

Yes No

You can change your answer later.

Test the repair

Flush two or three times. Wait sixty seconds after each flush. Listen for running water. Good: tank stabilizes, complete silence. Bad: still runs—recheck flapper and float, or call a plumber.

Done

Call a plumber

Call a plumber if: you replaced the flapper and adjusted the float but it still runs; water leaks outside the tank; the flush valve seat is cracked; or the tank is cracked.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why does a toilet keep running after a flush?
Usually the flapper is not sealing properly against the flush valve seat, or the float is set too high and water spills into the overflow tube. Lift the tank lid and press down on the flapper—if the running stops, replace or adjust the flapper.
Can I fix a running toilet myself?
Yes. A new flapper costs about $5–15 and takes 10–15 minutes to install. Adjust the float so water stops about one inch below the overflow tube. Most running toilets can be fixed DIY.
When should I call a plumber for a running toilet?
Call a plumber if you have replaced the flapper and adjusted the float but the toilet still runs, or if you see water leaking outside the tank. Also call if the flush valve seat is cracked or the tank is cracked.

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