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Toilet Keeps Running? The 4 Causes and How to Fix Each

A toilet that runs between flushes is almost always leaking water from the tank into the bowl, so the fill valve keeps topping it up. It can waste 200 gallons a day and add $20–$70 to a monthly water bill. The fix is usually a $5–10 part.

Verdict: DIY

One of the easiest repairs in the house. No tools beyond your hands for most causes.

Time
15–30 min
Cost
$5–25 in parts

Likely causes and how to tell

  • Worn or warped flapper

    Put 5 drops of food coloring in the tank and wait 15 minutes without flushing. Color in the bowl means the flapper leaks. This is the cause about 8 times out of 10.

  • Water level set too high

    Water trickles into the overflow tube (the open pipe in the middle of the tank). The level should sit about 1 inch below the top of that tube.

  • Chain too short or tangled

    The flapper doesn't close all the way after a flush, or the chain is caught under it.

  • Failing fill valve

    You hear a hiss or the tank refills in short bursts every few minutes even with a new flapper, or the valve won't shut off.

How to fix it

  1. 1

    Shut off the water

    Turn the oval valve behind the toilet clockwise until it stops, then flush and hold the handle to empty the tank.

  2. 2

    Do the dye test

    Before replacing anything, confirm where the leak is with food coloring (see causes). It saves you buying the wrong part.

  3. 3

    Replace the flapper

    Unhook the chain, slide the old flapper's ears off the pegs on the overflow tube, and take it to the store to match size (2-inch or 3-inch). Hook the new one on and leave about ½ inch of slack in the chain.

  4. 4

    Adjust the water level

    Turn the adjustment screw or slide the float clip on the fill valve so the water stops about 1 inch below the top of the overflow tube.

  5. 5

    Replace the fill valve if needed

    Disconnect the supply line under the tank, unscrew the locknut, lift the old valve out, and install a universal fill valve set to the height marked on your overflow tube.

  6. 6

    Test

    Turn the water on, let the tank fill, and repeat the dye test. No color after 15 minutes means it's fixed.

What you'll need

  • Replacement flapper (2" or 3")
  • Universal fill valve (if needed)
  • Adjustable wrench
  • Sponge and bucket
  • Food coloring

Call a pro if

  • Water is leaking onto the floor around the base (wax ring or cracked tank).
  • The shutoff valve behind the toilet won't turn or leaks when you touch it.
  • The tank or bowl has a visible crack.

AI Handyman writes a free job brief in trade language, so a pro can quote from your photos.

Questions people ask

How much water does a running toilet waste?

A steady leak can waste 200 gallons or more a day. Even a silent flapper leak adds up to thousands of gallons a month.

Is a universal flapper OK?

Usually, but match the size (2-inch or 3-inch drain). Some brands like Toto and newer Kohler models use specific seals, so bring the old one to the store.

Why does my toilet run for a few seconds every so often?

That's called phantom flushing: a slow flapper leak lets the level drop until the fill valve kicks in. Replace the flapper.

Related fixes

General guidance, not a licensed inspection. Follow local codes; when in doubt, call a licensed professional.