Why Is My Toilet Running? Causes, Checks, and Fixes

September 11, 2026 Corvellis Editorial

A toilet that runs between flushes can waste water silently. EPA WaterSense recommends checking toilets for leaks at least annually and notes that an old or worn flapper is a common cause.

Start With the 10-Minute Dye Test

Put a few drops of food coloring into the toilet tank and wait about 10 minutes without flushing. If color appears in the bowl, water is leaking from the tank into the bowl. Flush immediately after the test to avoid staining.

Common Reasons a Toilet Keeps Running

Worn or poorly sealing flapper

The flapper seals the tank after a flush. Rubber can wear, deform, or accumulate mineral deposits. EPA recommends checking it periodically and replacing the flapper at least every five years to help maintain a good seal.

Chain problem

A chain that is too short can prevent the flapper from closing fully, while excessive slack can interfere with operation. Compare the setup with the toilet manufacturer's instructions before adjusting it.

Water flowing into the overflow tube

If the tank water level is too high or the fill valve does not shut off correctly, water may continue into the overflow tube. EPA specifically identifies continuous flow into the overflow tube as a sign that the toilet needs further investigation.

Damaged flush-valve seal or other components

If a new correctly fitted flapper does not solve the problem, the leak may involve the flush-valve seat, fill valve, seals, or another component.

Simple Troubleshooting Sequence

Remove the tank lid carefully and observe what happens after a flush.
Perform the dye test.
Check whether the flapper closes flat and seals.
Check that the chain is not holding the flapper open.
Look for continuous water entering the overflow tube.
Use the toilet manufacturer's replacement-part guidance before changing components.

When to Call a Plumber

Get professional help if water is leaking onto the floor, the shutoff valve does not work, the toilet is loose, the bowl or tank is cracked, the problem persists after straightforward maintenance, or there are drainage symptoms elsewhere in the home.

Running Toilet FAQ

How do I know if my toilet has a silent leak?

Use EPA's dye test: add food coloring to the tank, wait about 10 minutes without flushing, and check whether color appears in the bowl.

How often should a toilet flapper be replaced?

EPA WaterSense recommends replacing it at least once every five years to help maintain a good seal, although wear or water conditions can require earlier replacement.

Should I replace the entire toilet?

Not necessarily. Many running-toilet problems involve replaceable tank components. If the toilet itself needs replacement, EPA recommends considering a WaterSense-labeled model.