Why is my toilet running constantly?

A constantly running toilet is often due to a faulty flapper or fill valve. The flapper may not be sealing properly, or the fill valve isn't shutting off the water supply, both of which are usually easy to fix yourself.

How do I know if I need to replace the flapper?

If you suspect a faulty flapper, add a few drops of food coloring into the toilet tank. If the colored water appears in the toilet bowl without flushing, the flapper is likely leaking and needs to be replaced.

What tools do I need for basic toilet repairs?

For most DIY toilet repairs, you'll need a wrench, pliers, a screwdriver, a new flapper (if that's the issue), and possibly a new fill valve. It's also a good idea to have a sponge and a bucket handy to clean up any water.

When should I call a plumber instead of trying to fix the toilet myself?

Call a plumber if you're dealing with a severely clogged toilet that you can't clear with a plunger or toilet snake, if there are cracks in the toilet bowl or tank, or if you're uncomfortable disassembling parts of the toilet.

How do I replace a toilet flapper?

First, turn off the water supply to the toilet. Next, detach the chain connecting the flapper to the flush lever. Then, remove the old flapper, attach the new one, and reattach the chain, adjusting the length as needed.

Fix a Running Toilet

By Home Sidekick Team June 14, 2025 9 min read 1767 words

toiletrepairplumbingdiyhome improvementrunning toilet

A running toilet is more than just an annoying sound. It's a constant drain on your water bill, and if left unchecked, it can waste hundreds of gallons of water. Fortunately, many running toilet issues are simple to fix yourself, saving you the cost of a plumber. This guide provides a step-by-step approach to diagnosing and repairing a running toilet, empowering you to tackle this common household problem.

Understanding the Anatomy of a Toilet

Before diving into repairs, it's helpful to understand the basic components of a toilet tank. Knowing the names and functions of each part will make troubleshooting and repairs much easier.

Tank: The reservoir that holds water for flushing.
Bowl: The lower part of the toilet that receives waste.
Flapper: A rubber or silicone seal at the bottom of the tank that lifts to release water into the bowl during a flush. This is a common culprit in running toilet issues.
Fill Valve (Ballcock): The mechanism that refills the tank after a flush. It includes a float that rises with the water level and shuts off the water supply when the tank is full.
Float: A ball or cylinder connected to the fill valve that rises with the water level, signaling the valve to shut off.
Overflow Tube: A vertical tube inside the tank that prevents overflowing if the fill valve fails to shut off.
Flush Valve: The opening at the bottom of the tank where the flapper sits.
Chain: Connects the flush handle to the flapper, lifting the flapper when the toilet is flushed.

Diagnosing the Cause of a Running Toilet

The first step in fixing a running toilet is to identify the cause. Here's a systematic approach to diagnosing the problem:

1. The Flapper is the Primary Suspect

The flapper is the most common cause of a running toilet. Over time, it can become worn, cracked, or warped, preventing a tight seal against the flush valve. To check the flapper:

Turn off the water supply: Locate the shut-off valve behind the toilet (usually near the floor) and turn it clockwise to shut off the water.
Flush the toilet: This will empty the tank.
Examine the flapper: Look for any signs of damage, such as cracks, wear, or mineral buildup. Feel the flapper's surface; it should be smooth and pliable.
Check the flapper chain: Ensure the chain is not too long (preventing the flapper from sealing) or too short (holding the flapper open slightly).
Inspect the flush valve seat: Clean any debris or mineral buildup from the flush valve seat where the flapper rests. A rough surface can prevent a good seal.

2. Investigate the Fill Valve and Float

If the flapper appears to be in good condition, the next suspect is the fill valve or float. Issues with these components can cause the tank to overfill, leading to water flowing into the overflow tube.

Observe the water level: Watch the water level in the tank after a flush. If it rises above the overflow tube, the fill valve is not shutting off properly.
Check the float: Make sure the float is moving freely and is not obstructed by anything inside the tank.
Adjust the float: Most floats can be adjusted to control the water level. There are generally two types of floats:

Ball float: Connected to the fill valve by a metal arm. Bend the arm slightly up or down to adjust the water level.
Cylinder float: Slides up and down the fill valve. Adjust the clip or screw on the float rod to change the water level.

Inspect the fill valve: Look for any signs of damage or wear on the fill valve. Mineral buildup can also interfere with its operation.

3. Overflow Tube Check

While the overflow tube itself isn't usually the direct cause of a running toilet, it's important to make sure it's functioning correctly. Its purpose is to prevent the tank from overflowing if the fill valve fails. Make sure the overflow tube is not cracked or damaged.

Repairing a Running Toilet: Step-by-Step Guides

Once you've diagnosed the problem, you can proceed with the repair. Here are detailed instructions for common fixes:

1. Replacing the Flapper

A worn or damaged flapper is a common issue that is easily rectified.

Turn off the water supply: As before, shut off the water supply to the toilet.
Flush the toilet: Empty the tank completely.
Detach the old flapper: Disconnect the chain from the flush lever arm and unhook the flapper from the mounting pegs on the flush valve.
Install the new flapper: Hook the new flapper onto the mounting pegs and connect the chain to the flush lever arm.
Adjust the chain: Make sure the chain has a little slack but is not so long that it prevents the flapper from sealing properly.
Turn on the water supply: Slowly turn the water supply back on and observe the water level in the tank. Flush the toilet a few times to ensure the flapper is sealing correctly.

Tip: Take the old flapper with you to the hardware store to ensure you purchase a compatible replacement. There are universal flappers available, but a direct replacement is often a better choice.

Example: I recently fixed my running toilet by replacing the flapper. The old one was cracked and brittle. The new flapper cost less than $10 and took only 5 minutes to install.

2. Adjusting or Replacing the Fill Valve

If the fill valve is the culprit, you may be able to adjust it or you might need to replace the entire unit.

Turn off the water supply: Shut off the water to the toilet.
Flush the toilet: Empty the tank.
Adjust the float: If the water level is too high, try adjusting the float as described earlier. This may solve the problem without replacing the fill valve.
Replace the fill valve (if necessary): If adjusting the float doesn't work, you'll need to replace the fill valve.

Disconnect the water supply line: Use a wrench to disconnect the water supply line from the bottom of the fill valve. Have a small bucket handy to catch any remaining water.
Remove the old fill valve: Most fill valves are held in place by a locknut underneath the tank. Use a wrench to loosen and remove the locknut. You may need to use pliers to hold the fill valve in place from inside the tank.
Install the new fill valve: Insert the new fill valve into the hole in the bottom of the tank and secure it with the locknut. Tighten the locknut firmly but avoid overtightening, which could crack the tank.
Connect the water supply line: Reconnect the water supply line to the bottom of the new fill valve.
Adjust the float: Adjust the float to the correct water level.
Turn on the water supply: Slowly turn the water supply back on and check for leaks. Flush the toilet several times to ensure the fill valve is working correctly.

Tip: When replacing the fill valve, consider upgrading to a newer, more efficient model. Dual-flush valves, for example, allow you to choose between a full flush and a half flush, saving water.

Research: According to the EPA, toilets account for nearly 30% of residential water consumption. Replacing an old, inefficient toilet or upgrading the fill valve can significantly reduce water usage. EPA WaterSense

3. Cleaning the Flush Valve Seat

Sometimes, mineral buildup or debris on the flush valve seat can prevent the flapper from sealing properly. Cleaning the seat can resolve the running toilet issue.

Turn off the water supply: Shut off the water to the toilet.
Flush the toilet: Empty the tank.
Dry the flush valve seat: Use a clean cloth or sponge to dry the flush valve seat thoroughly.
Clean the seat: Use a scrub brush or sandpaper to gently remove any mineral buildup or debris from the seat. Be careful not to scratch or damage the surface.
Rinse the seat: Rinse the seat with clean water to remove any remaining debris.
Reinstall the flapper: Reinstall the flapper and chain.
Turn on the water supply: Slowly turn the water supply back on and check for leaks. Flush the toilet several times to ensure the flapper is sealing correctly.

Preventative Maintenance for Toilets

Preventing problems is always easier than fixing them. Here are some tips for maintaining your toilet and preventing running toilet issues:

Regularly inspect the flapper: Check the flapper for signs of wear or damage every few months and replace it as needed.
Clean the toilet tank periodically: Mineral buildup can accumulate in the tank over time. Clean the tank every year or two to prevent problems. You can use a toilet bowl cleaner or a mixture of vinegar and water.
Avoid flushing non-flushable items: Only flush toilet paper and human waste. Flushing other items, such as feminine hygiene products, diapers, or wipes, can clog the toilet and damage the components.
Check the water pressure: High water pressure can put unnecessary stress on the toilet components. If your water pressure is too high, consider installing a pressure regulator.

When to Call a Plumber

While many running toilet issues can be fixed yourself, there are some situations where it's best to call a plumber:

You've tried the above steps and the toilet is still running: If you've replaced the flapper and fill valve, adjusted the float, and cleaned the flush valve seat, and the toilet is still running, there may be a more complex problem.
The toilet is leaking: If you notice water leaking from the base of the toilet or from the tank, it's important to call a plumber to prevent water damage.
You're uncomfortable working with plumbing: If you're not comfortable working with plumbing, it's always best to call a professional. A plumber can quickly diagnose and repair the problem, ensuring that the job is done correctly.

Conclusion: Stop the Run, Save Water, and Save Money

A running toilet might seem like a minor annoyance, but it can lead to significant water waste and higher water bills. By understanding the components of a toilet, diagnosing the cause of the problem, and following the step-by-step repair guides in this article, you can often fix a running toilet yourself. Regular maintenance and preventative measures can help prevent future issues. If you're unable to resolve the problem yourself, don't hesitate to call a qualified plumber.

Next Steps:

Inspect your toilet for signs of a running issue.
Identify which of the components described above is causing the problem.
Gather the necessary tools and replacement parts.
Follow the repair steps outlined in this article or call a plumber.