How to Diagnose a Running Toilet

  • 01 of 05

    Start by Removing the Tank Lid

    Start by opening the toilet tank.
    Start by opening the toilet tank. Aaron Stickley

    The annoying sound of a running toilet can be maddening, but the cause is fairly easy to understand: this ongoing trickle occurs when the water supply valve (usually known as a ballcock) does not shut off at the end of the flush cycle. What you are hearing is the water continuing to pour through the flush valve at the bottom of the tank and down into the toilet bowl. 

    It is more than just an annoyance because a constantly running toilet can waste hundreds of gallons of water if left unattended. 

    Th...MOREis symptom has three possible causes:

    • The water supply valve is misadjusted so it doesn't sense the water level in the tank properly. A simple adjustment can often fix this problem. 
    • The water supply valve itself is faulty and is failing to shut off at the end of the flush cycle. A complete replacement of the valve--or in some cases the seals within the valve--is the course of action. 
    • The flush valve (flapper) at the bottom of the toilet tank is failing to seal properly, thereby allowing water to continue to flow down into the tank. Since the water level can never reach the level required for the water supply valve to shut off automatically, the toilet continues to run endlessly. 

    Before you run to the hardware store to buy parts follow the following steps to find which of these problems is actually causing the symptom. 

    Begin by taking the lid off the toilet tank. 

    Continue to 2 of 5 below.
  • 02 of 05

    Step 1--Check the Overflow Valve

    Check the toilet overflow tube for running water.
    Check the toilet overflow tube for running water. Aaron Stickley

    The overflow tube is the round vertical cylinder in the center of the tank. As you watch, if you see water continuing to flow down over the lip of the tube, it's possible that the ballcock (water supply valve) simply needs to be readjusted so it shuts off when the water level is at a  lower level. The method for adjusting a water supply valve varies quite a bit, so you'll need to study your particular valve to figure out how it is done.

    But it's rather unusual for a water supply valve to...MORE suddenly be misadjusted if it's been working properly until recently. It's much more likely that the supply valve is simply worn out and needs to be replaced


    Continue to 3 of 5 below.
  • 03 of 05

    Check the Flapper Chain

    Look inside toilet tank to see if the flapper chain is causing the toilet to run.
    See if the flapper chain is causing the running water. Aaron Stickley

    If the overflow is not the problem, you’ll want to check the flapper chain next. This is the chain that connects the toilet's flush lever with the flapper flush valve at the bottom of the tank.

    If this chain is too short, it may not be allowing the flapper to drop down fully into the opening of the flush valve at the end of the flush cycle. This will allow water to continue flowing down into the tank, which in turn means the water supply valve will continue to run on delivering more water into...MORE the tank.

    On the other hand, if the chain is too long, it may bunch up under the flapper, preventing it from sealing after the flush cycle. 

    On either case, the fix is simply to adjust the lift chain so it is neither too long nor too short.


    Continue to 4 of 5 below.
  • 04 of 05

    Inspect the Flapper Seal

    Adding food coloring to toilet tank as a way to check the flapper's seal.
    Check the flapper's seal by adding food coloring to the toilet tank. Aaron Stickley

    The third possibility is the flapper itself. As the flapper gets old it, can get so hard or warped that it can no longer provide a good seal. Even a slight imperfection could be causing the toilet to run. A few drops of food coloring can let you know if this is the problem.

    Add the food coloring to the toilet tank and give it a few minutes. If you see coloring trickling down into the bowl, you will need to ​​replace the toilet flapper

    Continue to 5 of 5 below.
  • 05 of 05

    Repair Tips

    Colored water in toilet bowl.
    Food coloring from the toilet tank runs into the bowl if the flapper doesn't seal. Aaron Stickley

    Any coloring in the toilet bowl will let you know that the flapper is not sealing and needs to be replaced. Replacing the flapper (flush valve) is not a difficult job; just by a replacement that looks like the old one. 

    If you find yourself doing one of these repairs in your toilet and it's clear the parts are older, you might consider using this opportunity to "remodel" the inside of your toilet by installing all new parts. Sooner or later, all the internal parts of a toilet will...MORE wear out, and when you find yourself needing to replace one, it's a good bet that others will soon need replacing, too. You can save yourself future work by proactively replacing all toilet parts at the same time. Inexpensive kits are available that offer both the flapper valve and water supply valve together.