How to Fix a Running Toilet

Lower your water bill with these straightforward steps to stop a running toilet.

bathroom white toilet marble sink patterned tile floor
Photo: Tria Giovan
Project Overview
  • Skill Level: Beginner
  • Estimated Cost: $50

Over time, a toilet can begin to run continuously or intermittently, resulting in increased water usage bills. Not to mention, the regular sound of running water can quickly get frustrating to hear. However, fixing this issue isn't overly complicated. Taking the time to troubleshoot the fill valve assembly and flush valve assembly will help you determine the exact cause of the problem.

Make sure that if you need to replace any parts during this repair you find compatible parts for your toilet. If you aren't experienced with DIY plumbing jobs, the process of replacing some of the parts of the toilet might seem complicated, but by discovering how a toilet functions and the various parts that could be causing this issue, you can learn how to fix a running toilet.

Understanding How a Toilet Functions

The first step to fixing a running toilet is to learn how a toilet actually operates. Most people know that water fills up the toilet tank and when the toilet is flushed, this water gets emptied into the toilet bowl to force waste and wastewater into the drain line. However, the exact details of how this occurs are often unknown to the average individual.

Water flows through the water line and up into the tank of the toilet using the fill valve tube. The water is trapped in the tank by the flapper, a large gasket that sits at the bottom of the tank and is typically attached to the base of the flush valve.

As the tank fills with water, the float rod or float cup is forced to rise. When the float reaches a set level, the fill valve stops the flow of water into the tank. If the toilet has a faulty fill valve, the water might continue to rise until it spills into the overflow tube, which is intended to prevent accidental flooding.

With the toilet tank full, the toilet can be flushed with the lever or flush button, which pulls on a chain to lift the flapper. The water then flows out of the tank at a great enough force to keep the flapper open as the water rushes into the toilet bowl through the holes evenly spaced around the rim. Some toilets also have a secondary entry point called a siphon jet that increases flushing power.

This flood of water increases the water level in the toilet bowl, allowing it to flow into the S-trap and through the main drain line. When the tank is empty, the flapper settles back into place to seal the tank as water begins to flow back into the tank through the fill valve.

Determine Why the Toilet is Running

Toilets are not overly complex, but there are several parts that can cause your toilet to run, so it's necessary to troubleshoot the issue before you can resolve the problem. A running toilet is typically caused by the overflow tube, flush valve, or fill valve.

Check the water in the tank to determine if it is running into the overflow tube. If the water is running into the overflow tube, the water level might be too high or the overflow tube might be too short for the toilet. The water level can be adjusted to resolve this issue, but if the overflow tube is too short, the entire flush valve assembly will need to be replaced.

The running water is likely caused by the fill valve if the problem persists despite the overflow tube being the right height for the toilet and the water level being set about an inch below the top of the overflow tube.

If the water is not running into the overflow tube, then it is usually the flush valve assembly that is causing the issue. The chain could be too short, preventing the flapper from fully closing, or the flapper might be warped, worn, or coated in grime, resulting in water flowing through the gap and into the tank.

blue gold ostrich wallpaper bathroom with tile floor
Jay Wilde

What You'll Need

Equipment / Tools

  • Channel locks
  • Screwdriver


  • Bucket
  • Towel, cloth, or sponge
  • Float
  • Flapper
  • Flush valve
  • Fill valve
  • Flush valve chain


A constantly running toilet isn't just an annoyance; it's also a costly waste of water that you will end up paying for on your next water bill. To resolve this problem, identify the part that is causing the issue and take the necessary measures outlined below.

  1. Check the Overflow Tube Height

    The overflow tube is a part of the flush valve assembly. If the current flush valve assembly isn't compatible with the toilet, the overflow tube might be too short. The tube could also have been cut too short during installation. If the overflow tube is too short, causing the water to run continuously, you will need to replace the flush valve assembly with a compatible flush valve. However, if the overflow tube is the right height for the toilet, then the issue might be the water level or the fill valve.

  2. Lower the Water Level in the Tank

    Ideally, the water level should be set to about an inch below the top of the overflow tube. If the water level is set higher than this, it's recommended to lower the water level by adjusting the float rod, float cup, or float ball. Float rods and float balls typically extend out from the side of the fill valve, while a float cup is a small cylinder that is attached directly to the fill valve where it slides up and down with the water level.

    To adjust the water level, locate the screw that attaches the float to the fill valve and use a screwdriver or a set of channel locks to turn the screw about a quarter-turn counterclockwise. Continue to make quarter-turn adjustments until the float is set to the desired water level. Keep in mind that if water is trapped inside the float, it will sit lower in the water, leaving the fill valve partially open. Correct this issue by replacing the float.

    If the water continues running until it flows into the overflow tube, regardless of the float level, then the issue is probably caused by a faulty fill valve. However, if the water is continuously running but not flowing into the overflow tube, then the flush valve might be the problem.

  3. Inspect the Flush Valve Chain

    The flush valve chain is intended to lift the flapper in response to the toilet lever or flush button being used. If the flush valve chain is too short, the flapper will not be able to close properly, resulting in a steady stream of water constantly flowing through the toilet. Similarly, if the chain is too long, it can get trapped underneath the flapper, preventing it from closing.

    Check the flush valve chain to make sure it's the right length to allow the flapper to fully close without extra links of chain that could become an obstruction. You can shorten the chain by removing several links until it's the right length, but if the chain is too short you might need to get a replacement flush valve chain to resolve the problem.

  4. Check the Flapper

    The flapper is typically made of rubber and can become warped, worn, or coated in grime over time. Inspect the flapper for any signs of significant wear, warping, or grime. If the flapper is damaged, replace it with a new flapper. If it's just dirt, simply clean the flapper with a solution of warm water and vinegar.

  5. Replace the Flush Valve

    After inspecting the overflow tube, the water level setting, the length of the flush valve chain, and the current state of the flapper, you might find that the problem is caused by the actual flush valve assembly. Purchase a compatible flush valve assembly online or from a local home improvement store to ensure the new overflow tube will be tall enough for the toilet tank.

    Start the replacement process by turning off the water to the toilet using the isolation valve on the water inlet line. Next, flush the toilet to drain the water and use a cloth, towel, or sponge to remove any remaining water from the tank. Disconnect the water supply to the tank using a set of channel locks.

    You need to detach the toilet tank from the toilet bowl to remove the old flush valve assembly. Remove the tank-to-bowl bolts and carefully lift the tank off the toilet to access the toilet-to-bowl gasket. Loosen the flush valve nut and remove the old flush valve assembly, setting it aside in a nearby sink or bucket.

    Install the new flush valve in its place, then tighten the flush valve nut and replace the tank-to-bowl gasket before putting the tank back into position. Secure the tank-to-bowl bolts and reconnect the water supply to the toilet. Turn the water back on and allow the tank to fill up. While it's filling, take the time to check for any leaks at the base of the tank. If the water continues to run after the tank is full, then the tank-to-bowl gasket or the flapper might be improperly installed.

  6. Replace the Fill Valve

    If you find that the overflow tube is the right height for the toilet and the water level is set about an inch below the overflow tube, but water continues to flow into the overflow tube, the issue is likely the fill valve. Replacing the fill valve isn't as difficult as dealing with a faulty flush valve.

    Turn off the water to the toilet using the isolation valve on the water inlet line, then flush the toilet to empty the tank. Use a cloth, towel, or sponge to soak up any remaining water, then remove the water supply line with a set of channel locks. Unscrew the locking nut on the bottom of the tank to loosen the fill valve assembly.

    Remove the old fill valve assembly and set it aside in a sink or bucket, then install the new fill valve assembly. Adjust the height of the fill valve and float to ensure it sits at the correct level for the toilet. Secure the fill valve assembly with the locking nut on the bottom of the tank. With the new fill valve in place, reattach the water supply line and turn the water back on. Check the bottom of the tank and the water supply line for leaks as the tank fills with water. If the repair was successful, the water will stop flowing into the tank when the float reaches the set level instead of continuing to fill until it spills into the overflow tube.

When to Contact a Plumber

Even if you have some experience with DIY tasks, like woodworking or landscaping, you might not fully understand the various parts of a toilet and how they work together to create a functional fixture for waste management. If the steps above seem too complex or you are nervous about attempting a plumbing repair on your own, it's recommended to contact a professional plumber to fix the issue. Trained professionals might cost more, but they ensure that the work is done quickly, safely, and effectively so you don't have to worry about potential problems, like cutting the overflow tube too short or a leaking toilet tank.

Frequently Asked Questions

  • How do you fix a running toilet without a ball float?

    More modern toilets have a fill valve instead of a ball float, which is actually easier to fix. To fix a toilet with a fill valve, first examine the valve and corresponding float cup to see if either (or both) are installed correctly. If so, and the issue still persists, you'll likely need to replace the fill valve and the float cup to stop the tank from overflowing.

  • How do you fix a running toilet with a button flush?

    If your toilet has a button flush (also known as a dual flush toilet) and is continuously running, you want to start by cleaning or replacing the seal. If the issue continues—or if the water level is high and close to overflowing—you may need to replace the fill valve.

  • How much does it cost to fix a running toilet?

    Fixing a running toilet is typically a very inexpensive project, sometimes costing under $50. However, if you need to hire a plumber—or if your running toilet is the sign of a larger plumping issue—costs can increase significantly. Depending on the complexity of the fix, a plumber may charge $75 to $400 to repair a running toilet.

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