Why Is My Toilet Leaking or Running Constantly?

If your toilet keeps running or you notice water leaking into the bowl, the problem is usually inside the tank. In many cases, a leaking toilet is caused by a worn flapper, an improperly set float, or a failing fill valve. The good news is that these issues are often easy to diagnose.

TL;DR

• A leaking or running toilet is usually caused by the flapper, float, or fill valve.
• If water flows into the overflow tube, the float is set too high.
• If water leaks slowly into the bowl, the flapper may not be sealing.
• Food coloring can help confirm a flapper leak.
• If repairs feel uncomfortable, a professional plumber can fix the issue quickly.

How a toilet works

Understanding how a toilet works makes it easier to find the source of a leak. When you push the handle, a rod lifts the flapper inside the tank. The flapper opens and allows tank water to flow into the toilet bowl.

The flapper floats briefly because it traps air. As the tank empties, the flapper sinks back into place and seals the opening again.

The tank then refills using a float attached to the fill valve. As the water level rises, the float shuts off the incoming water. At the same time, a small tube sends water into the bowl to refill it.

Check the water level first

If the water level inside the tank is above the overflow tube, water will continuously drain into the bowl. This prevents the float from ever shutting off the water supply.

You can fix this by adjusting the float. Most toilets have an adjustment screw on the fill valve. Turning it lowers the float and reduces the water level. Older models may require gently bending the float rod.

The final water level should always sit below the top of the overflow tube.

Test the flapper for leaks

A common cause of a running toilet is a flapper that no longer seals properly. To test this, add a few drops of food coloring to the tank and wait about five minutes.

If colored water appears in the bowl, the flapper is leaking and should be replaced. Flappers are inexpensive and widely available.

If your toilet uses a tank ball instead of a flapper, make sure the vertical rod allows it to sit squarely over the drain opening.

Check the chain and connections

If your toilet uses a flapper with a chain, make sure the chain has enough slack. A chain that is too short or kinked can prevent the flapper from sealing completely.

Inspect the fill valve

If the flapper and float are working correctly, the fill valve may be worn. Some fill valves contain replaceable washers or O-rings. If these parts show any wear, replacing them may solve the problem.

If the fill valve is a sealed unit, the entire assembly will need to be replaced. This requires turning off the water supply, flushing the toilet, disconnecting the supply line, and removing the valve from the tank.

When to call a plumber

If you are uncomfortable working inside the tank, worried about causing damage, or simply do not want to deal with it, calling a professional plumber is a smart choice.

An experienced plumber can diagnose a leaking toilet quickly and complete the toilet repair without guesswork.