Why does my toilet keep running?

The short answer

The short answer

A toilet that keeps running is letting water leak from the tank into the bowl, and a worn flapper is the most common cause. Add a few drops of food coloring to the tank and wait 15 minutes without flushing. If color shows up in the bowl, replace the flapper. If it doesn't, check the fill valve and the water level in the tank.

The three most common causes

The flapper. This rubber seal at the bottom of the tank lets water into the bowl when you flush. Over time it hardens, warps or collects mineral buildup from hard water, so it no longer seals tightly. It's the most common cause of a running toilet.

The fill valve. This refills the tank after each flush. If it doesn't shut off, the water rises above the overflow tube and keeps draining into the bowl. You'll usually hear a steady trickle or hiss.

The water level. Sometimes nothing is broken: the float is just set too high, so water spills into the overflow tube. Lowering the float costs nothing and is worth checking before you buy parts.

The dye test

Remove the tank lid and add a few drops of food coloring to the water in the tank. Don't flush. Wait about 15 minutes, then look in the bowl.

If you see color in the bowl, water is leaking past the flapper, and the flapper needs replacing. If there's no color but the toilet is still running, water is likely flowing into the overflow tube, which points to the fill valve or the float setting.

This quick test tells you which repair you need, and it's free.

Why it's worth fixing soon

A running toilet can waste hundreds of gallons of water a day, often without making much noise. Many people only notice when their water bill goes up for no clear reason.

If your water bill has jumped and your usage hasn't changed, try the dye test on every toilet in the house first. It's the same first step we take, and it rules out a simple fix before moving on to leak detection.

When to call a plumber

If you've replaced the flapper and the toilet still runs, the valve seat the flapper rests on may be worn or scaled. That repair usually means removing the tank, so it's a good time to call us.

If water is collecting on the floor around the base of the toilet, turn off the water at the shutoff valve behind the toilet. That usually means a failed wax ring or flange, not a tank problem, and using the toilet will keep pushing water under the floor. Our fixture repair page explains what that repair involves.

And if your toilet is more than 20 years old and keeps needing parts, replacing it is often the better investment.