DIY Guides

How to Fix a Running Toilet (Step-by-Step with Photos)

Updated 2026-03-10

How to Fix a Running Toilet (Step-by-Step with Photos)

Always verify contractor licensing and insurance in your state. Cost estimates are averages and may vary by location.

A running toilet wastes up to 200 gallons of water per day and can add $100 or more to your monthly water bill. The good news is that this is one of the simplest plumbing repairs a homeowner can do, with parts costing under $15 and no special skills required.

Three Common Causes

Almost every running toilet traces back to one of three parts inside the tank.

1. Worn Flapper

The flapper is the rubber seal at the bottom of the tank. When it deteriorates, water leaks continuously from the tank into the bowl.

How to diagnose: Add a few drops of food coloring to the tank water. Wait 15 minutes without flushing. If colored water appears in the bowl, the flapper is leaking.

[PHOTO PLACEHOLDER: Flapper location inside toilet tank]

2. Faulty Fill Valve

The fill valve controls water entering the tank after a flush. When it malfunctions, it runs continuously or cycles on and off (phantom flushing).

How to diagnose: Lift the float arm while the toilet is running. If the water stops, the fill valve or float needs adjustment or replacement.

[PHOTO PLACEHOLDER: Fill valve and float arm identification]

3. Incorrect Overflow Tube Height

If the water level in the tank rises above the overflow tube, water continuously drains into the bowl, triggering the fill valve to run.

How to diagnose: Look inside the tank. If water is flowing into the top of the overflow tube, the water level is set too high.

[PHOTO PLACEHOLDER: Overflow tube with water level markings]

Tools and Parts Needed

  • Adjustable pliers or channel-lock pliers
  • Replacement flapper ($3 to $7)
  • Replacement fill valve ($8 to $12, if needed)
  • Sponge and towel
  • Bucket

Total cost: under $15 for most repairs.

Fix 1: Replace the Flapper

  1. Turn off the water supply valve behind the toilet.
  2. Flush the toilet to empty the tank. Sponge out remaining water.
  3. Unhook the old flapper from the overflow tube ears.
  4. Disconnect the flapper chain from the flush lever.
  5. Attach the new flapper to the overflow tube ears.
  6. Connect the chain to the flush lever, leaving about half an inch of slack.
  7. Turn the water supply back on and let the tank fill.
  8. Flush and check for leaks. Repeat the food coloring test to confirm the seal.

[PHOTO PLACEHOLDER: Step-by-step flapper replacement sequence]

Fix 2: Replace or Adjust the Fill Valve

  1. Turn off the water supply and flush the tank.
  2. Place a towel under the supply line connection.
  3. Disconnect the supply line from the old fill valve.
  4. Unscrew the locknut under the tank and remove the old valve.
  5. Adjust the new fill valve height to match your tank (the critical level mark should sit one inch above the overflow tube).
  6. Insert the new valve through the tank hole and hand-tighten the locknut.
  7. Reconnect the supply line.
  8. Attach the refill tube to the overflow tube.
  9. Turn on the water and adjust the float to set the water level about one inch below the overflow tube top.

[PHOTO PLACEHOLDER: Fill valve replacement steps]

Fix 3: Adjust the Water Level

If the water level is too high and running into the overflow tube:

  1. For a ball float, turn the adjustment screw on the float arm clockwise to lower the float.
  2. For a cup float (integrated into the fill valve), pinch the spring clip and slide the float down the valve shaft.
  3. The correct water level is marked on the inside of most tanks. Aim for about one inch below the overflow tube.

[PHOTO PLACEHOLDER: Float adjustment comparison — ball vs cup style]

When to Call a Plumber

Call a professional if:

  • The toilet base leaks onto the floor (this indicates a wax ring failure, not a tank issue).
  • You hear water running inside the wall.
  • The shut-off valve behind the toilet is seized or leaking.
  • Replacing the flapper and fill valve does not stop the running.

A plumber visit for a running toilet typically costs $130 to $225. See Home Repair Cost Estimator (Interactive Calculator) for more pricing data, or visit Get Free Repair Quotes to get quotes from local professionals.

Key Takeaways

  • A running toilet almost always comes down to the flapper, fill valve, or water level.
  • The food coloring test quickly identifies a flapper leak.
  • Parts cost under $15, and the repair takes 15 to 30 minutes.
  • If basic fixes do not solve the problem, a plumber can diagnose deeper issues.

Next Steps