Why Does My Toilet Keep Running? How to Find and Fix It
A running toilet can waste hundreds of gallons a day, and the fix is usually a part that costs less than a pizza. Here is how to tell which part has failed.
Quick answer
Lift the tank lid. If water is spilling into the open overflow tube, the float is set too high or the fill valve is failing. If the water level is below the tube but the toilet keeps refilling, water is leaking past the flapper into the bowl, usually because the flapper is worn or the chain is too short. Both are inexpensive DIY repairs.
- Difficulty
- Easy DIY
- Water wasted
- Up to about 200 gallons a day
- Most common cause
- Worn flapper
- Test
- Food coloring in the tank, wait 10 minutes
- Typical parts
- Flapper or fill valve
On this page
A toilet tank works like a simple machine. Flushing lifts a rubber flapper and lets the tank empty into the bowl. The flapper drops back onto its seat, and a fill valve refills the tank until a float tells it to stop. A running toilet means one of those steps is not finishing.
Find the leak in five minutes
- Look at the water level.
Remove the tank lid and set it somewhere safe; they break easily. If water is pouring into the top of the overflow tube, skip to “Float set too high.” If the level is below the top of the tube, continue.
- Do the dye test.
EPA WaterSense recommends adding a few drops of food coloring to the tank and waiting 10 minutes without flushing. If color appears in the bowl, water is leaking past the flapper. Flush afterward so the dye does not stain.
- Watch a flush.
Check that the chain is not tangled or caught under the flapper, that the flapper drops cleanly onto its seat, and that the handle springs back.
The five causes and how to fix them
1. Worn or warped flapper
The most common cause. Rubber flappers harden, warp and pick up mineral deposits, so they no longer seal. Close the shutoff valve behind the toilet, flush to drain the tank, unhook the old flapper from the pegs on the overflow tube, and take it to the store to match it. Flappers come in 2-inch and 3-inch sizes; check the size printed on the old one or measure the drain opening.
2. Chain too short, too long or tangled
A chain that is too short holds the flapper slightly open. One that is too long can get trapped under the flapper. Adjust it so there is about half an inch of slack when the flapper is closed, and trim any excess.
3. Float set too high
If the float lets the water rise above the top of the overflow tube, water spills into the bowl constantly. Lower the float so the water stops about an inch below the top of the overflow tube, or at the water line marked inside the tank. Modern fill valves have a cup-style float adjusted by a screw or clip on the side; older ones use a ball on an arm you can bend or adjust.
4. Failing fill valve
If the water keeps rising even with the float lowered, or the valve hisses and refills on its own, the fill valve is worn. Replacement fill valves are universal for most toilets and come with instructions. This takes longer than a flapper but needs only basic tools.
5. Refill tube pushed down into the overflow
The small flexible tube from the fill valve should clip to the top of the overflow tube, not reach down into it. If it is pushed too far in, it can siphon water out of the tank continuously.
| What you see | Cause | Fix |
|---|---|---|
| Water spilling into the overflow tube | Float too high or fill valve failing | Lower the float; replace the fill valve if it continues |
| Dye reaches the bowl | Leaking flapper | Replace the flapper |
| Toilet refills by itself every so often | Slow flapper leak | Replace the flapper |
| Flapper does not close after a flush | Chain too short or caught | Adjust the chain |
| Hissing with level below the overflow | Fill valve or refill tube | Reposition the tube; replace the valve |
Check the shutoff valve before you need it. If the small valve behind the toilet is stuck or leaks when you turn it, do not force it. You can shut off water at the main valve while you work, and have a plumber replace the stop valve.
When to call a plumber
- Water is leaking onto the floor from the base of the toilet or the tank bolts.
- The tank or bowl is cracked.
- The shutoff valve will not close or leaks.
- New parts do not stop the running, which can point to a worn flush valve seat.
Frequently asked questions
How much water does a running toilet waste?
EPA WaterSense estimates that a leaking toilet can waste about 200 gallons of water every day. A toilet that runs nonstop can waste even more.
Why does my toilet run for a few seconds every so often?
That is called a phantom flush. Water slowly leaks past the flapper into the bowl until the tank level drops enough to trigger the fill valve. Replacing the flapper usually stops it.
How often should a toilet flapper be replaced?
EPA WaterSense suggests checking flappers periodically and replacing them at least every five years, since the rubber degrades, especially in water treated with chlorine or chloramine.
Can I fix a running toilet without turning off the water?
Adjusting the float or chain does not require it. To replace a flapper or fill valve, close the shutoff valve behind the toilet and flush to empty the tank first.
Sources
- Fix a Leak Week U.S. EPA WaterSense
- Home Maintenance U.S. EPA WaterSense
- Toilet Leak Detection NYC Department of Environmental Protection
First published October 6, 2026. Last reviewed October 6, 2026. Spot an error? Tell us and we will check it against the source.