How to Fix a Running Toilet: 5 Easy DIY Fixes

A Running Toilet Is Costing You More Than You Think

That constant trickle of water flowing from the tank into the bowl is money going straight down the drain. A continuously running toilet can waste 200 gallons of water per day -- over 6,000 gallons per month. Depending on your local water rates, that translates to an extra $50 to $200 on your monthly water bill.

The good news is that most running toilet repairs take 15 to 30 minutes and cost less than $25 in parts. This guide walks you through the five most common causes and exactly how to fix each one.

How a Toilet Works: The 30-Second Version

Understanding the flush cycle helps you pinpoint the problem:

1. You press the handle, which lifts the flapper (the rubber seal at the bottom of the tank) off the flush valve seat.
2. Water rushes from the tank into the bowl, creating the flush.
3. Once the tank is nearly empty, the flapper drops back down and seals the opening.
4. The fill valve turns on and begins refilling the tank with fresh water.
5. As the water level rises, the float (either a ball on an arm or a cup that rides the fill valve shaft) rises with it.
6. When the float reaches the preset level, it signals the fill valve to shut off.

A running toilet means something in this cycle has broken down -- water is either leaking past the flapper into the bowl, or the fill valve is not shutting off.

The Dye Test: Confirm Your Toilet Is Running

Before replacing parts, run a simple dye test to determine whether the flapper is leaking:

1. Remove the tank lid and set it on a towel.
2. Drop 5 to 10 drops of food coloring into the tank water.
3. Do not flush. Wait 15 minutes.
4. Check the bowl. Colored water in the bowl means the flapper is leaking. Clear water means the issue is likely with the fill valve or float.

What You Will Need

Most repairs require only basic tools and inexpensive parts: an adjustable wrench or channel-lock pliers, a sponge and bucket, rubber gloves, a towel, food coloring, a tape measure, white vinegar, and a non-abrasive scrub pad. Depending on the fix, you may also need a replacement flapper ($5 to $10) or a fill valve replacement kit ($10 to $20).

Fix 1: Replace the Flapper

The flapper is the most common cause of a running toilet, responsible for roughly 80 percent of cases. Over time, the rubber warps, cracks, or develops mineral buildup that prevents it from sealing tightly against the flush valve seat.

How to Identify a Bad Flapper

• The dye test shows colored water in the bowl (water is leaking past the flapper).
• The flapper looks warped, cracked, stiff, or feels slimy when you touch it.
• The toilet runs intermittently, stopping and starting on its own (sometimes called a "phantom flush"). This happens because the tank slowly leaks down to a level that triggers the fill valve to refill.

Step-by-Step Flapper Replacement

1. Turn off the water supply. Locate the shut-off valve on the wall behind the toilet. Turn it clockwise to shut off the water.
2. Flush the toilet to drain most of the water. Hold the handle down to let as much water out as possible, then sponge out the rest into a bucket.
3. Remove the old flapper. Most flappers have two rubber ears that hook onto pegs on either side of the overflow tube. Unhook the ears and disconnect the chain from the flush lever arm.
4. Match the replacement. Take the old flapper to the hardware store, or buy a universal flapper (such as the Fluidmaster 502 or Korky 100BP), which fits most standard toilets.
5. Install the new flapper. Hook the rubber ears onto the overflow tube pegs. Connect the chain to the flush lever arm, leaving about 1/2 inch of slack. Too much slack and the flapper will not lift fully; too little and it will not seat properly.
6. Turn the water back on, let the tank fill, and flush a few times to confirm the toilet stops running. Repeat the dye test to verify the seal.

Cost: $5 to $10 for a universal flapper. Time: 10 to 15 minutes.

Fix 2: Adjust the Float

If the dye test shows no leak past the flapper but water is trickling into the overflow tube, the water level in your tank is set too high. The float controls where the fill valve shuts off. When the float is set too high, the water level rises above the overflow tube, and excess water continuously drains into the bowl.

Ball Float vs. Cup Float

Older toilets use a ball float -- a round plastic or rubber ball attached to a horizontal metal or plastic arm connected to the fill valve. Newer toilets use a cup float -- a small cylindrical float that slides up and down directly on the fill valve shaft.

How to Lower the Water Level

For a ball float:

1. Locate the ball float arm extending from the top of the fill valve.
2. If the arm is metal, gently bend it downward about 1/2 inch. This lowers the point at which the float triggers the valve to shut off.
3. If the arm has an adjustment screw where it connects to the fill valve, turn the screw clockwise to lower the float level.
4. Flush and check. The water level should stop about 1 inch below the top of the overflow tube. The tank will usually have a water line mark molded into the porcelain as a guide.

For a cup float:

1. Locate the adjustment clip or screw on the float assembly (it rides on the fill valve shaft).
2. Squeeze the clip and slide the float downward on the shaft, or turn the adjustment screw counterclockwise to lower it.
3. Flush and check. Again, the water should stop about 1 inch below the overflow tube opening.

Cost: Free -- no parts needed. Time: 5 minutes.

Fix 3: Replace the Fill Valve

If the fill valve hisses constantly, vibrates, or simply will not shut off regardless of the float position, the valve itself is worn out and needs to be replaced. Fill valves have internal seals and diaphragms that degrade over time.

Signs of a Bad Fill Valve

• A constant hissing sound coming from the tank, even after the tank has filled.
• The valve does not shut off no matter how you adjust the float.
• Water sprays or squirts erratically from the top of the valve.
• The valve is visibly corroded or the parts feel gritty.

Step-by-Step Fill Valve Replacement

1. Turn off the water supply and flush the toilet. Sponge out remaining water and place a bucket under the tank.
2. Disconnect the water supply line from the bottom of the fill valve using an adjustable wrench or channel-lock pliers.
3. Remove the old fill valve. Unclip the refill tube from the overflow tube, then reach under the tank and unscrew the lock nut. Lift the old valve straight up and out.
4. Adjust the new valve height. Most replacement valves (such as the Fluidmaster 400A or Korky 528) are adjustable. Set the height so the top of the valve sits about 1 inch above the overflow tube.
5. Insert the new valve through the hole in the bottom of the tank. Hand-tighten the lock nut from underneath, then give it an additional half turn with pliers. Do not over-tighten -- you can crack the porcelain.
6. Reconnect the supply line and tighten the coupling nut. Clip the small rubber refill tube to the top of the overflow tube.
7. Turn on the water, let the tank fill, and adjust the float so the water level stops about 1 inch below the overflow tube. Flush several times to verify the valve shuts off cleanly.

Cost: $10 to $20 for a fill valve kit. Time: 20 to 30 minutes.

Fix 4: Check and Trim the Overflow Tube

The overflow tube is the large vertical tube in the center of the tank. It prevents the tank from overflowing by directing excess water into the bowl. The water level should stop at least 1 inch below the top of the overflow tube.

If adjusting the float (Fix 2) does not bring the water below the overflow tube, the tube itself may need attention:

• Too short or too low. If the tube sits too low, water reaches the top even at the correct fill level. You may need to replace the entire flush valve assembly (the overflow tube and flapper seat are one unit).
• Cracked. A hairline crack lets water leak continuously. Inspect the tube carefully. A cracked tube requires replacing the full flush valve assembly.
• Too tall. If the tube extends so high that the tank lid presses on it, mark it with a marker and trim to the correct height with a hacksaw -- typically about 1 inch below the tank lid opening and at least 1 inch above the desired water line. Smooth rough edges with fine sandpaper.

Cost: Free if trimming only; $15 to $30 for a flush valve assembly replacement. Time: 10 minutes for trimming; 45 to 60 minutes for a full replacement.

Fix 5: Clean the Flush Valve Seat

Sometimes the flapper itself is in good condition, but mineral deposits, sediment, or grime on the flush valve seat prevent the flapper from creating a watertight seal. This is especially common in areas with hard water.

How to Clean the Flush Valve Seat

1. Turn off the water and flush the toilet to empty the tank.
2. Remove the flapper by unhooking the ears from the overflow tube pegs.
3. Inspect the flush valve seat -- the flat ring at the bottom of the tank where the flapper sits. Run your finger along it. You may feel rough spots, mineral buildup, or grit.
4. Scrub the valve seat with a non-abrasive scrub pad (such as a Scotch-Brite pad) and white vinegar until it feels smooth and even. Also clean the underside of the flapper.
5. Reinstall the flapper, turn the water back on, and run the dye test. If colored water still appears in the bowl, the valve seat may be pitted and the flapper should be replaced.

Cost: Free if you already have vinegar and a scrub pad. Time: 10 minutes.

When to Call a Plumber

Most running toilet problems can be solved with basic tools and a hardware store trip. However, call a licensed plumber if:

• The porcelain tank or bowl is cracked. A cracked tank will leak onto the floor and only get worse.
• The toilet wobbles or rocks. This usually means the wax ring seal or floor flange has failed, which can cause water damage and sewer gas leaks.
• You smell sewage. Sewer odors indicate a seal failure or venting problem that requires professional diagnosis.
• Multiple fixes have not worked. If you have replaced the flapper, adjusted the float, and swapped the fill valve without success, a plumber can identify less obvious issues like a warped valve seat.
• The shut-off valve will not turn. Do not force it -- it may break and cause a flood. A plumber can replace the valve safely.

If you need help finding a qualified plumber, request a free quote through our contact page.

Quick-Reference Summary

Start with the dye test, work through the fixes in order, and you will likely solve the problem in under 30 minutes for less than $25. If the issue turns out to be more than a simple part swap, reach out to a licensed plumber before a small problem becomes an expensive one.