Why Does My Toilet Keep Running?

A running toilet is easy to ignore, but it can quietly waste a lot of water, and in Phoenix that shows up on the bill. The good news: almost every running toilet comes down to one of three parts inside the tank.

Find the cause in five minutes

1. Take the lid off the tank and look at the water level. If water is spilling into the overflow tube (the open pipe in the middle), the fill valve is set too high or failing.
2. If the level looks fine, put a few drops of food coloring in the tank. Don’t flush. Wait 15 to 20 minutes.
3. If color shows up in the bowl, water is leaking past the flapper at the bottom of the tank.
4. Check the chain from the handle to the flapper. Too short and the flapper can’t seal; too long and it can get caught under the flapper.

Why it happens

• Flappers are rubber, and they warp, stiffen and wear out over time. Hard water speeds that up.
• Mineral buildup on the flush valve seat keeps a flapper from sealing, even a new one.
• Fill valves wear out and stop shutting off cleanly, so you hear the toilet refill on its own.

What you can safely try

Turn the water off at the shutoff valve behind the toilet before you work in the tank. Adjust the chain so it has a little slack, or lower the float on the fill valve so the water stops about an inch below the top of the overflow tube. If the flapper is the problem, take the old one to the store so you get a match.

When to call us

Call if the shutoff valve won’t turn or drips, if a new flapper still leaks, if water is on the floor around the base, or if you would rather not deal with it. We replace flappers, fill valves, shutoff valves and supply lines, and reset or replace whole toilets. See our plumbing repairs.

Last reviewed November 1, 2026. This guide is general information. When in doubt, or for anything involving gas, wiring or major water damage, call a professional.