How to Fix a Running Toilet depends on which of two failures you have: water escaping over the top of the overflow tube, or water leaking past the flapper at the bottom of the tank. Both live inside the tank, both are cheap to fix, and a ten-minute check tells you which one you have. Start with the most likely culprit — a worn flapper — then check the chain, the water level, and the fill valve, in that order. Most people fix this with one part costing under $15 and no plumber.
One warning: a running toilet can waste 200 gallons of water a day or more, according to the EPA’s WaterSense program. If you can’t fix it today, turn the oval shutoff valve behind the toilet clockwise to stop the waste.
The Parts Inside Your Tank
You only need to know five parts:
- Flapper — the rubber plug at the bottom of the tank; it lifts when you flush and drops back to seal the tank.
- Flush valve — the opening under the flapper, with a rim (the seat) the flapper seals against.
- Overflow tube — the open pipe in the middle of the tank; if water rises too high, it drains down this tube into the bowl instead of flooding the floor.
- Fill valve — the unit on the left that refills the tank after a flush and shuts the water off.
- Float — a ball on an arm, or a cup on the fill valve; it tells the valve when the tank is full.
Step 1: Diagnose It in 10 Minutes
Take the tank lid off and set it on a towel — porcelain lids crack on tile.
Look first. Flush and watch. If water pours over the overflow tube, your problem is on the fill side: the level is set too high, or the fill valve is not shutting off. Skip to causes 3 and 4.
Then run the dye test. If the level looks normal but the toilet refills on its own every few minutes, or you hear a faint hiss, water is probably leaking past the flapper. Put food coloring in the tank, do not flush, and wait 10 to 15 minutes. Color in the bowl means the flapper or its seat is leaking. This is the test the EPA recommends for silent leaks, and it costs nothing.
A second check, from Fluidmaster’s guide: with the tank full, turn the water off, mark the level with a pencil, and wait 10 to 15 minutes. If it dropped, water is leaving through the flapper or flush valve; if not, the problem is on the fill side.
Cause 1: A Worn Flapper (Most Common)
The flapper sits in tank water around the clock. Chlorine, minerals and time make it warp, stiffen or turn slimy, and then it cannot seal. Water seeps past it, the level drops, the fill valve tops it up, and the cycle repeats — the hiss at night, and the reason the toilet refills by itself.
How to check: Unhook the flapper and run a finger over its underside. It should feel smooth and flexible; if it feels rough, stiff or warped, or leaves black residue, replace it. Wipe the flush valve seat while you are there — grit on the seat breaks the seal too.
How to fix it (about 10–15 minutes, no tools): Turn the shutoff valve clockwise and flush to empty the tank. Unhook the chain, remove the old flapper, and take it to the store — flappers come in 2-inch and 3-inch sizes, and matching the old one is the surest way to get the right fit. Clip the new flapper on, reconnect the chain with about half an inch of slack, turn the water on, and flush two or three times, watching the flapper drop flat each time. Cost: roughly $5–$15. Flappers are wear parts — plan on replacing one every 3 to 5 years, sooner with in-tank bleach tablets, which attack the rubber. Fluidmaster warns that drop-in bleach or chlorine tablets damage tank parts and can void its warranty.
Cause 2: The Chain Is Too Tight, Too Loose, or Caught
The chain needs about half an inch of slack. Too tight, and it holds the flapper a fraction open — enough for a constant leak. Too long, and the loose end can slip under the flapper and stop it sealing. Unhook it, straighten it, and reattach it with a little slack; trim the excess. If running stops when you jiggle the handle, check the handle nut too — usually reverse-threaded, so it tightens counterclockwise. Cost: free. Time: five minutes.
Cause 3: The Water Level Is Too High
If water spills into the overflow tube, check where the fill valve shuts off: the water should stop about an inch below the top of the tube, or at the waterline stamped inside the tank. On a float-cup valve, turn the screw on top, or squeeze the clip and slide the cup down a little. On a ball float, turn the screw at the valve end of the arm, or bend the arm down gently. Flush after each small adjustment. Cost: free. Time: five to ten minutes.
Cause 4: The Fill Valve Is Dirty or Worn Out
If the level is set correctly and water still pours into the overflow tube, or the valve hisses and never shuts off, the fill valve is failing. Sediment can lodge inside it, and the seal under the cap wears out. Typical life is 5 to 8 years.
Try cleaning it first (10 minutes): Turn the water off and flush. Twist the cap off the valve top, hold an upside-down cup over the open valve, and turn the water on briefly to flush out grit. Replace the cap and test. If its seal looks worn or cracked, a replacement costs a few dollars.
If cleaning does not work, replace the valve (about 20–30 minutes): turn the water off, flush, and sponge out the tank. Disconnect the supply line over a bucket, unscrew the locknut under the tank, and lift the old valve out. Set the new valve’s height so its critical level mark sits about an inch above the overflow tube top, per the kit. Tighten the locknut hand-tight plus a quarter turn — no more, because the tank is porcelain. Reconnect the supply line, clip the refill tube to the overflow tube, turn the water on, and set the level. Cost: about $10–$25. Tools: adjustable wrench or pliers, sponge, bucket.
Cause 5: The Refill Tube Is Pushed Too Far Down
The refill tube is the small flexible tube from the fill valve to the overflow tube. It should clip onto the top of the tube with its end above the water line. Pushed down inside, below the water level, it can siphon water out of the tank and keep the valve cycling. Pull it up, clip it in place, and retest. Cost: free.
Cause 6: The Flush Valve Seat Is Damaged, or the Overflow Tube Is Cracked
If a new flapper still leaks, feel the seat it seals against. Mineral crust wipes off, but a pitted, cracked or uneven seat will not seal with any flapper. A crack in the overflow tube below the waterline also drains the tank continuously.
Fixing either one means replacing the flush valve — on a two-piece toilet, that means removing the tank. This is also where Fluidmaster’s troubleshooting route ends: if a new flapper still leaks, replace the flush valve. A kit costs roughly $15–$30 and the job takes about an hour.
How to replace it (about 1 hour): Turn the water off, flush, and sponge out the tank. Disconnect the supply line over a bucket, unscrew the tank bolts underneath, and lift the tank onto a towel. Unscrew the large locknut, lift the old valve out, and wipe the opening clean. Seat the new valve with its gasket (kit instructions for overflow height) and tighten the locknut hand-tight plus half a turn at most, per Fluidmaster — more can crack the porcelain. Fit a new tank-to-bowl gasket and bolt washers, set the tank back, and tighten the bolts a little at a time, alternating sides, until level and snug. Reconnect everything, set the level, and re-run the pencil-mark test. It is the biggest job on this page — if it sounds like too much, this is where a plumber earns his fee.
Water under the tank is a bolts-and-gasket problem. Drips at the tank bolts mean the tank-to-bowl gasket or bolt washers have failed — Fluidmaster’s guide gives the same verdict. The fix uses the same tank removal, then new bolts, washers and gasket, tightened evenly. If the bolts are rusted solid, or the tank is cracked, stop and call a plumber. A supply-line drip is a different small job, covered in how to fix a leaky faucet.
Button-flush toilets: most dual-flush and canister-style toilets have no flapper. A rubber canister seal at the base of the flush tower does the same job and wears the same way; if water trickles into the bowl, clean or replace that seal, using the model number inside the tank.
Check That the Fix Worked
Silence is not proof — a slow leak can be completely quiet. Repeat the pencil-mark test: fill the tank, turn the water off, mark the level, wait 15 minutes. No drop means the leak is gone. A water meter’s leak indicator should also stay still while no water is being used.
What does fixing a running toilet cost?
| Fix | DIY parts cost | Typical time |
|---|---|---|
| Chain adjustment, float adjustment, refill tube | $0 | 5–10 minutes |
| New flapper | $5–$15 | 10–15 minutes |
| Fill valve cleaning / new seal | $0–$5 | 10 minutes |
| New fill valve | $10–$25 | 20–30 minutes |
| New flush valve (tank removal) | $15–$30 | About 1 hour |
Part prices are typical US retail ranges as of November 2026. Hire it out, and Angi’s 2026 cost data puts a professional repair at roughly $100–$400, including the call and labor — the whole argument for trying the flapper first.
When to Call a Plumber
- You have replaced the flapper and the fill valve, and it still runs — likely the flush valve or something upstream.
- The shutoff valve will not turn, or leaks when you touch it. Forcing a seized valve can crack it and flood the bathroom.
- The tank is cracked, or there is water on the floor around the base — usually a failed wax ring or tank-to-bowl leak, a bigger repair. Standing water also ruins grout and flooring; see how to clean grout lines once the leak is stopped.
- You are not comfortable removing the tank.
Mistakes That Keep a Toilet Running
- Buying the wrong flapper size. A 2-inch flapper on a 3-inch valve will never seal. Take the old one to the store.
- Leaving the chain with no slack. It holds the flapper open just enough to leak around the clock.
- Overtightening the locknut. Hand-tight plus a quarter turn; more can crack the tank.
- Using drop-in bleach tablets. They eat flappers and seals, and at least one major manufacturer voids its warranty over them.
- Setting the water level too high “for a stronger flush.” Water above the overflow tube just runs down the drain.
- Assuming quiet means fixed. Always re-run the dye or pencil-mark test after a repair.
Frequently Asked Questions
Why does my toilet run every few minutes, then stop? That is phantom flushing (also called ghost flushing). A slow leak past the flapper lowers the tank level until the fill valve tops it up. Run the dye test; if color reaches the bowl, replace the flapper and clean the seat.
Why does my toilet keep running right after I flush? Usually the flapper is not dropping back into place — a tangled or too-short chain, or a warped flapper landing crooked. Lift the lid, flush, and watch it fall. If it looks stiff or misshapen, replace it.
Is a running toilet an emergency? Not usually, but do not leave it for weeks: at up to 200 gallons a day (EPA estimate), it adds real money to a water bill. Shut the water off until you fix it, and call a plumber promptly if there is water on the floor.
I replaced the flapper and it still runs. Now what? Check the new flapper matches your valve size, the chain is not caught under it, and the seat is smooth. If all three are fine and water spills into the overflow tube instead, the problem is the float setting or the fill valve.
How much water does a running toilet waste? The EPA’s WaterSense program puts a running toilet at 200 gallons a day or more. A slow, silent leak wastes less, but still adds up to thousands of gallons over a year.
Does this guide cover pressure-assisted or flushometer toilets? No. This guide covers tank toilets. A pressure-assisted toilet has a sealed vessel inside the tank, and a flushometer toilet has no tank at all; both use different parts and different fixes, so follow that manufacturer’s instructions instead of the flapper and fill-valve steps above.
Should I replace an old toilet instead of repairing it? Sometimes. If the toilet is old, uses far more per flush than a current WaterSense model (1.28 gallons), and needs more than a flapper or fill valve, replacement can be the better spend. If it only runs, repair first — the parts above cost under $30.
How long should a flapper last? Around 3 to 5 years in typical tap water; chlorine, hard water and bleach tablets shorten that. If a flapper feels stiff, warped or slimy, replace it regardless of age — it is a $5–$15 part.
Sources: Fluidmaster troubleshooting, EPA WaterSense leak data, and Angi’s 2026 cost data. Prices are typical ranges, not quotes.