Your place · Basic home repairs

Fixing a running toilet

Most running toilets are one of two things: a worn flapper letting water leak into the bowl, or a fill valve or float set so high that water spills down the overflow tube. A dye test tells you which. Set the water about 1/2 inch below the top of the overflow tube, give the flapper chain about 1/2 inch of slack, and replace a warped flapper. Skip bleach tablets in the tank, since they eat the rubber parts.

Easy20 to 40 min to doUsually just the price of a flapper or a fill valveChecked October 2, 2026

Do it like this

If dye reaches the bowl, it's usually the flapper.

Listen and look first. A toilet should only make noise while it refills after a flush. Water still moving in the bowl long after the tank has filled, or a need to jiggle the handle, means a leak. Source: Clay-Battelle Public Service District
Do the dye test. Lift the tank lid, add a few drops of food coloring to the tank, and don't flush. If color shows up in the bowl within 10 to 20 minutes, you have a leak. Source: EPA WaterSense Clay-Battelle PSD The faster it shows, the bigger the leak. Flush afterward so the dye doesn't stain.
Figure out which part is failing. Mark the water level on the inside back wall of the tank with a pencil. Flush and watch it refill. If the water rises above your mark and then drops, it's probably the flapper. If it keeps rising and spills into the overflow tube, it's probably the fill valve. Source: Clay-Battelle PSD
Fill valve or float problem: lower the water. Adjust the float (a screw or clip on the fill valve, or the arm on an old float ball) so the water stops about 1/2 inch below the top of the overflow tube. Source: Fluidmaster If it still won't shut off, the fill valve can stick open and needs replacing. Source: Clay-Battelle PSD
Flapper problem: check the chain first. With the handle down, the chain should have about 1/2 inch of slack. Source: Fluidmaster Too tight, and the flapper can't seal. Too long, and it can get caught under the flapper.
Replace the flapper. Turn off the valve behind the toilet (clockwise), flush to empty the tank, and sponge out the rest. Source: Fluidmaster Unhook the chain from the handle lever, slip the old flapper off the pegs on the overflow tube, and hook on the new one. Reattach the chain with a little slack.
Test it. Turn the water back on, let the tank fill, flush a few times, and run the dye test again.

Watch out If the toilet is about to overflow, turn the valve behind it clockwise to stop the water first, then deal with the rest. If you rent, a leaking toilet is usually your landlord's repair. Report it in writing, and ask before you replace parts.

What's wrong, and the fix

From a water utility's leak guide and the manufacturer's instructions. Source: Clay-Battelle PSD Fluidmaster

What you see	Likely cause	Fix
Dye leaks into the bowl, and the tank refills by itself now and then	Warped or damaged flapper, or a chain or lever out of line	Adjust the chain to about 1/2 inch of slack. If that doesn't fix it, replace the flapper.
Water spills into the overflow tube nonstop	Fill valve stuck open, or water level set too high	Lower the float so water stops 1/2 inch below the tube's top. Replace the fill valve if it still runs.
Still leaks with a new flapper	Grit or damage on the flush valve seat the flapper sits on	That's a bigger repair. Call a plumber, or your landlord if you rent.
Runs at night or while you're away	Higher overnight water pressure can push a float-ball valve open	Replace an old float-ball valve with a newer piston-style fill valve.
Rust stains inside the bowl	Corroding metal parts in the tank	Run the dye test to find the leak, then fix it.

See it done

How to Repair Toilet Tank Components This Old House Commercial publisher · Length 4:24 · 2020 · Checked October 2, 2026

Video blocked on this network? You don't need it. The written steps are the whole lesson, and the video is extra. Watch it on YouTube later.

If it doesn't work

Flapper doesn't fit? Not every replacement flapper fits every water-saving toilet. Bring the old one with you, and look for one with a five- or ten-year warranty. Source: Clay-Battelle PSD
Replacing a float-ball fill valve? Use a newer piston-style fill valve instead of another float ball. Source: Clay-Battelle PSD
Valve behind the toilet won't turn? Don't force it. Use the home's main shutoff Source: Regional Water Providers Consortium and call a plumber or your landlord.
Going away for a week or more? Turning off the water to each toilet before you leave prevents a leak from running the whole time. Source: Clay-Battelle PSD
Toilet clogged, not running? Use a flange plunger, never a chemical drain cleaner. See Clearing a clogged drain.

Good to know

Skip the bleach tablets

In-tank cleaners with bleach or chlorine can damage the flapper and other tank parts and void the warranty. Source: Fluidmaster Clay-Battelle PSD

Why bother

Worn toilet flappers are one of the most common household leaks, and the average household's leaks waste more than 9,300 gallons a year. Source: EPA WaterSense A stuck-open fill valve can run 3 to 5 gallons a minute. Source: Clay-Battelle PSD

Check your bill

Look at a winter month's water use. The EPA says a family of four using more than 12,000 gallons a month likely has a serious leak. Source: EPA WaterSense

It adds up nationwide

Household leaks waste nearly 900 billion gallons of water a year across the country. Source: EPA WaterSense

Sources

U.S. Environmental Protection Agency Fix a Leak Week
U.S. Environmental Protection Agency WaterSense statistics and facts
Clay-Battelle Public Service District Repair your leaking toilets (PDF)
Fluidmaster Company source: manufacturer instructions 555C flush valve and flapper installation instructions (PDF)
Fluidmaster Company source: manufacturer instructions 400A fill valve installation instructions (PDF)
Regional Water Providers Consortium Emergency water shut-off

Lesson H4.2 · Last checked October 2, 2026 against the sources listed.

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