How to Stop a Toilet From Running Constantly

3 Most Common Causes & Repairing Them Yourself

Flushing toilet bowl landscape
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Project Overview
  • Working Time: 20 mins - 1 hr, 30 mins
  • Total Time: 30 mins - 2 hrs
  • Skill Level: Intermediate
  • Estimated Cost: $10 to $30

As DIY tasks go, fixing a running toilet can be relatively easy, though many beginners may have trouble taking apart the toilet and putting it back together, which is why this project is better suited to individuals with some plumbing experience. Typically, a running toilet can be caused by issues with three main parts inside the tank:

  • The first part is designed to prevent the toilet tank from overflowing and it is aptly named the overflow tube.
  • The second problem part is the flush valve, which is responsible for releasing the water inside the tank when the toilet is flushed. The most common reason a toilet continues to run involves the flush valve, and fortunately this is one of the most easy repairs for a DIYer.
  • Finally, the third part that may be causing the toilet to run is the fill valve.

If you need to replace any parts of the toilet during this repair, make sure to find compatible parts to avoid causing further issues. The cost is minimal for new parts and can help you save money on water bills in the future when the toilet stops running.


It may seem like a minor problem, but it's actually bad news for a toilet to keep running continuously. Unless the problem is addressed, it will never stop on its own. Your toilet may squander literally hundreds of gallons of water. Fortunately, stopping a toilet from running usually costs just a few dollars.

How a Toilet Works

To better comprehend why these problem parts cause the toilet to run, it's necessary to have a clear understanding of exactly how a toilet works. It's a fairly easy matter to understand a toilet's working parts by simply removing the tank lid and examining the parts inside:

  1. Water enters the toilet tank through the fill valve tube and it is prevented from exiting the tank by the flapper, which is a large gasket at the base of the flush valve that sits in the bottom of the tank.
  2. As the tank fills, the float rod rises with the water, and when it reaches the set water level, the fill valve stops the flow of water. If the water continues to rise beyond this point, it may begin to spill into the overflow tube, which is designed to prevent flooding by draining water before the tank can overflow.
  3. At this point, the toilet can be flushed. Pressing down on the handle or button pulls on a chain that is attached to the flush valve flapper. The flapper opens and releases the water inside the tank.
  4. The water rushes into the toilet bowl through evenly spaced rim holes and may have a secondary entry point known as a siphon jet to help increase flushing power.
  5. When the additional water enters the toilet bowl the water level increases, allowing it to flow through the trap and into the main drain.
  6. The water continues to flow until the tank is empty, then the flapper returns to its previous place, sealing the tank.

A constantly running toilet indicates that the system is either allowing water to pass continuously through the flush valve flapper or that the water within the tank is flowing into the overflow tube. You can quickly check whether the excess water is flowing into the toilet bowl or into the overflow tube by putting a few drops of dye into the tank.

If the colored water flows into the toilet bowl, then the issue is likely with the flush valve or flapper mechanism, but if the water in the toilet bowl remains clear, the problem is with the fill valve or overflow tube system.

What You'll Need

Equipment / Tools

  • Channel lock pliers
  • Bucket
  • Towel, cloth, or sponge
  • Screwdriver


  • Flush valve
  • Flush valve chain
  • Fill valve


If the Problem Is With the Overflow Tube

The overflow tube is a hollow tube that is connected to the flush valve. It's designed to prevent the toilet tank from overflowing if the fill valve does not turn off. There are several reasons why the water may be flowing into the overflow tube and causing the toilet to run.

  1. Check the Water Level

    The water level inside the toilet tank should always sit below the overflow tube and the fill valve to ensure that the water doesn't continuously flow into the tank and out through the overflow tube.

    Check the water level by removing the lid from the tank of the toilet and verifying whether or not the water level is too high, causing it to run into the overflow tube.

    If the water is running into the overflow tube, then the water level may need to be lowered, but if the water is not running into the overflow tube, then the issue is likely with the flush valve.

  2. Adjust the Float Rod or Float Cup

    To lower the water level inside the toilet tank, you will need to adjust the float rod or float cup. A float rod can be identified by the horizontal rod extending from the fill valve to a float ball, while a float cup is a small cylinder that wraps around the fill valve and slides up or down with the water level.

    You will need to locate the screw that attaches the float rod or float cup to the fill valve. Use a screwdriver, a set of channel locks, or pliers to turn this screw about a quarter-turn counterclockwise to lower the water level. Continue making adjustments until the water is no longer flowing into the overflow tube.

    If the water continues flowing, regardless of the position of the float rod or float cup, the issue is likely with the fill valve. However, if the water stops flowing, but the volume of water inside the tank is not enough to properly flush the toilet, then it's likely that the overflow tube is too short for the toilet.


    Water-logged floats can also cause constant running. If water is trapped inside your float, it will sit lower in the water and leave your float valve partially open. Check your float by unscrewing it (if applicable) and shaking it. Replace the float if you hear water inside. 

  3. Verify the Overflow Tube Height

    An overflow tube is intended to prevent the toilet tank from overflowing, but if it's too short, then the water will continuously flow into the tank and out of the overflow tube. This can occur if the flush valve is not compatible with the toilet, or if the overflow tube was cut too short during installation.

    If the overflow tube is too short, the only way to fix this issue is to replace the flush valve. Just make sure that the new flush valve is compatible with your toilet and that the overflow tube is taller than the old overflow tube to prevent water from draining continuously.

If the Problem Is With the Flush Valve

The flush valve is an assembly within the toilet that consists of an overflow tube, tank-to-bowl hardware, a tank-to-bowl gasket, a flapper, and a chain that connects to the flapper. The main purpose of a flush valve is to open the flapper to allow water to flow into the toilet bowl when the toilet is flushed and to close the flapper when the toilet tank is empty to allow the toilet tank to refill.

  1. Check the Chain

    A constantly running toilet is typically due to an issue with the flush valve assembly, so one of the first parts to inspect should be the chain and flapper.

    If the chain is too short, then it won't allow the flapper to close properly, but if it is too long it may get trapped underneath the flapper, causing it to leak. Verify that the chain is just the right length to allow the flapper to fully close and open without a lot of extra chain.

  2. Inspect the Flapper

    The next step is to inspect the flapper. These rubber parts can become warped, worn, or simply dirty over time and may not sit properly inside the flush valve seat. If any defects are found in the flapper, then it's a good idea to replace it, but if it appears to just be dirty, then the problem may be solved by washing it with a water and vinegar solution. Just make sure to turn off the water to the toilet and drain the tank before attempting to clean the flapper.

  3. Replace the Flush Valve

    If the water from the tank continues to seep into the toilet bowl, or you find that the overflow tube is too short, then the entire flush valve will need to be replaced.

    Turn off the water to the toilet using the isolation valve located on the water inlet line, then drain the toilet tank by flushing the toilet. Use a cloth or towel to dry up any remaining water before disconnecting the water supply to the tank with a set of channel locks.

    Take out the old flush valve by disconnecting the flapper and removing the tank-to-bowl bolts. Carefully lift the tank off of the toilet so that you can access the toilet-to-bowl gasket and loosen the flush valve nut. Consider having a partner to help make this process easier.

    Install the new flush valve, tighten the flush valve nut, and replace the tank-to-bowl gasket. Carefully put the tank back into place and reinstall the tank-to-bowl hardware. Reconnect the water supply to the toilet and turn the water back on. Check for any leaks at the base of the tank to avoid accidental water damage.

    Flush the toilet to test the new flush valve and then verify that the toilet stops running with the new part installed by allowing the toilet to fill up. If the water keeps running, then the tank-to-bowl gasket or the flapper may not be properly installed.

If the Problem Is With the Fill Valve

The fill valve controls the flow of water into the tank from the main water supply. It's designed to continue filling the toilet until the float arm or float cup reaches the set level, but a broken valve may continue running non-stop or may even turn on and turn off inconsistently. The excess water flows into the overflow tube, preventing the tank from overflowing, but the toilet will keep running.

  1. Verify the Fill Valve is Faulty

    To verify whether the issue is the fill valve, remove the top of the toilet tank and check the set water level, as well as the height of the overflow tube. If the overflow tube is an appropriate height for the toilet and the water level is set to about an inch below the top of the overflow tube, but the water continuously flows into the overflow tube, then the problem is the fill valve.

  2. Replace the Fill Valve

    Replacing the fill valve isn't as difficult as replacing the flush valve, though you will still need a set of channel locks and a cloth, towel, or sponge.

    Start the replacement by turning the water off to the toilet with the isolation valve on the water inlet line, then drain the tank by flushing the toilet. Soak up the excess water with a cloth, towel, or sponge to make sure the tank is dry before removing the water supply line with a set of channel locks.

    Take the old fill valve out by unscrewing the locking nut on the bottom of the tank and pulling the fill valve assembly out of the tank. Place the old fill valve in a sink or bucket to catch any excess water.

    Adjust the height of the new fill valve to suit the specific toilet tank and the desired water level, then insert the threaded end of the valve into the bottom of the tank. Secure it to the tank with a locking nut to create a watertight seal. 

    Reconnect the water supply, then turn the water back on. If the replacement was successful, the fill valve will immediately begin filling the toilet tank with water and will stop when the float arm or float cup reaches the set level. Check for leaks at the base of the toilet tank to avoid water damage.