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Fix a toilet that will not stop running

We'll confirm the symptom, check the flapper seal, adjust or replace the fill valve and float, or tell you when to call a plumber.

Troubleshooting · Home plumbing
10–20 min
What you'll need
  • Replacement flapper (if needed; universal flappers fit most toilets)
  • Towel to protect the lid and catch drips
  • Fine-grit sandpaper (optional; for rough flush valve seat)
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Steps

Goal: Confirm the symptom, check the flapper, adjust the float and fill valve, or call a plumber.

  • Listen for water running or trickling after you flush. Lift the tank lid and watch the water level.
  • Good: Water runs or trickles continuously—proceed to Check the flapper.
  • Bad: Toilet stops after fill—different issue; check for slow leak.

Check the flapper

Goal: Confirm whether the flapper is sealing. It is the most common cause of a running toilet.

  • Turn the shut-off valve behind the toilet clockwise to stop water flow.

  • Lift the tank lid and set it on a folded towel. Press down on the flapper with your finger.

  • Good: Running stops when you press—flapper is the cause. Replace it.

  • Bad: Running continues—check the float and fill valve.

  • Inspect the flapper for cracks, warping, or mineral buildup. Check the flush valve seat for roughness.

  • Replace the flapper if damaged. Unhook from the pegs, disconnect the chain, install the new flapper with half an inch of chain slack.

  • If the seat is rough, wipe with a cloth and fine-grit sandpaper before installing the new flapper.

Adjust the float and fill valve

Goal: Set the water level below the overflow tube and fix a faulty fill valve.

  • The water level should sit about one inch below the top of the overflow tube.
  • If water spills into the tube, the float is set too high. Turn the adjustment screw clockwise on a ball-cock float, or slide the clip down on a cylinder float.
  • Replace a cracked or waterlogged float.
  • If the fill valve dribbles or does not shut off, twist the top cap counterclockwise and rinse debris from the seal. Reassemble and test. If it still fails, replace the valve.

When to get help

Call a plumber if:

  • You have replaced the flapper and adjusted the float but the toilet still runs.
  • The flush valve seat is cracked or cannot be smoothed.
  • Water leaks outside the tank.
  • You are not comfortable working inside the tank.

Verification

  • The toilet stops running within a minute of flushing.
  • No water flows into the overflow tube after the tank fills.
  • No water leaks outside the tank.
  • You hear silence 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 continuously after flushing.
  2. Check flapper seal Inspect and replace the flapper if worn or warped.
  3. Adjust float and fill valve Set water level below overflow tube; replace fill valve if it will not shut off.
  4. Call a plumber Cracked seat, tank leak, or repeated failures—call a professional.

What to capture if you need help

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

  • Whether the flapper was replaced
  • Whether the float was adjusted
  • Whether the fill valve was replaced
  • Steps already tried

Does the toilet run continuously after flushing?

Listen for water running or trickling. Lift the tank lid and watch for water flowing into the overflow tube.

Listen after flushing. Lift the tank lid and check the water level. Good: water runs or trickles continuously—proceed to check flapper. Bad: toilet stops after fill—different issue; check for slow leak or phantom flush.

Yes No

You can change your answer later.

Does pressing the flapper down stop the running?

Press the flapper with your finger. If running stops, the flapper is not sealing.

Press down on the flapper. Stops: flapper is the cause—replace it. Continues: float or fill valve issue—proceed to check float.

Yes (stops) No (continues)

You can change your answer later.

Replace flapper and test

Replace the flapper with a universal or matching part. Reconnect the chain with half an inch of slack. Turn water back on and flush. The toilet should stop running. If it still runs, check the float and fill valve.

Done

Is water spilling into the overflow tube?

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

Check the water level. Spilling into tube: adjust the float down—turn screw clockwise or slide clip down. Not spilling: fill valve may not shut off—inspect and replace if needed.

Yes No

You can change your answer later.

Adjust float and test

Lower the float so water stops about one inch below the overflow tube. Flush and confirm the toilet stops running. If it still runs, replace the fill valve.

Done

Does the fill valve shut off when the tank is full?

The fill valve should shut off cleanly when the float reaches the set level.

Flush and watch the fill valve. If it dribbles or does not shut off, clean the seal or replace the valve. Reassemble and test. If it still fails, call a plumber.

Yes No

You can change your answer later.

Replace fill valve and test

Replace the fill valve with a matching part. Follow the manufacturer instructions. Turn water back on and flush. The toilet should stop running. If it still runs, call a plumber.

Done

Call a plumber

Call a plumber if you have replaced the flapper and adjusted the float but the toilet still runs, if the flush valve seat is cracked, if water leaks outside the tank, or if you are not comfortable working inside the tank.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why will my toilet not stop running?
Usually the flapper is not sealing against the flush valve seat, or the float is set too high and water spills into the overflow tube. The fill valve can also fail to shut off. Check the flapper first—it is the most common cause.
Can I fix a toilet that will not stop running myself?
Yes. Most running toilets are fixed by replacing the flapper or adjusting the float. Parts cost about $5–20. If the flush valve seat is cracked or the tank leaks, call a plumber.
When should I call a plumber for a toilet that will not stop running?
Call a plumber if you have replaced the flapper and adjusted the float but the toilet still runs, if the flush valve seat is cracked or rough and cannot be smoothed, or if water leaks outside the tank.

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