A toilet keeps running because water is leaving the tank faster than it should, so the fill valve keeps refilling it. Almost always, the water is escaping one of two ways: past a worn or misaligned flapper at the bottom of the tank, or over the top of the overflow tube because the water level is set too high. Lift the tank lid and you can usually tell which in a few minutes.
It’s worth fixing quickly. According to the EPA, the average household’s leaks can waste more than 9,300 gallons of water a year, and a running toilet is one of the most common culprits.
How the tank is supposed to work
When you push the handle, it pulls a chain that lifts the flapper, and the water in the tank rushes into the bowl. As the tank empties, the flapper drops back onto its seat and seals the opening. The fill valve then refills the tank, while a small refill tube sends some water down the overflow tube to top up the bowl. When the water reaches the right level, the float rises and shuts the fill valve off. A running toilet means one of those steps isn’t finishing.
Step 1: Look at the water level
Take the lid off and watch. If water is trickling into the top of the overflow tube, the level is set too high and the fill valve never gets the signal to stop. The water line should sit below the top of the overflow tube, usually about an inch, or at the line marked on the tube or tank. Lower the float: most modern fill valves have an adjustment screw or clip on the side; older ball-float arms can be bent down slightly.
Step 2: Do the dye test for the flapper
If the water isn’t going into the overflow tube, it’s probably leaking past the flapper. The EPA’s test:
- Put a few drops of food coloring in the tank.
- Don’t flush for about 10 minutes.
- If color appears in the bowl, the tank is leaking into it.
- Flush afterward so the dye doesn’t stain the tank.
A toilet that briefly refills on its own every so often, sometimes called a phantom flush, is the same problem: a slow leak past the flapper.
The common causes and fixes
A worn or warped flapper
Flappers are rubber, and over time they stiffen, warp or get coated with mineral deposits so they no longer seal. This is the most common cause. Replacement flappers are inexpensive, and the EPA suggests checking the flapper periodically and replacing it at least every five years. Take the old one to the store to match its size, since flappers come in different widths.
A chain that’s too short, too long or tangled
A chain that’s too tight holds the flapper slightly open. One that’s too long can get caught under the flapper. Leave a little slack, about enough that the chain hangs with a slight curve when the flapper is closed.
A dirty or worn flush valve seat
If a new flapper still leaks, the rim it sits on may be rough or crusted with minerals. With the water off and the tank drained, wipe the seat clean. A badly worn seat may need a repair kit or a new flush valve.
A failing fill valve
If the level is set correctly but water keeps hissing in and spilling into the overflow, the fill valve isn’t shutting off. Sometimes flushing out debris fixes it; often the simplest fix is a new fill valve.
A refill tube pushed too far down
The small refill tube should clip onto the top of the overflow tube. If its end sits below the water line inside the overflow tube, it can siphon water out of the tank continuously.
What you can fix yourself vs. when to call a plumber
| Safe for most homeowners | Call a plumber |
|---|---|
| Adjust the float and water level | A shutoff valve that won’t turn or that leaks |
| Adjust or replace the chain | A cracked tank or bowl |
| Replace the flapper | Water leaking around the base of the toilet |
| Reposition the refill tube | Leaks between the tank and bowl after you’ve tried the fixes |
| Replace the fill valve, if you’re comfortable | Replacing the flush valve, which usually means removing the tank |
Before you start. Turn the shutoff valve behind the toilet clockwise to close it, then flush to empty the tank. Set the heavy porcelain lid somewhere flat and safe, since it cracks easily. If the shutoff valve is stuck, don’t force it; old valves can break and leak.
Frequently asked questions
Does a running toilet raise my water bill?
Yes. Even a quiet leak runs all day and night, so it can add up to a noticeable amount of water over a billing period.
Why does jiggling the handle stop it?
Jiggling resettles a flapper that didn’t drop squarely, or frees a chain that got caught. It works for a moment, but it means the flapper or chain needs attention.
I replaced the flapper and it still runs. Now what?
Check that it’s the right size and sits centered, that the chain has slack, and that the valve seat underneath is clean. Then check the water level against the overflow tube.
Sources
- U.S. EPA WaterSense, Fix a Leak Week