Faucet Manual

Toilet keeps running: find whether it is the fill valve or the flapper

A running toilet is either overfilling into the overflow pipe or leaking out the bottom into the bowl. Four checks with the lid off tell you which, and which part to buy.

Toilet tank cross-section with the fill valve: cap about 3 inches above the overflow pipe, water line about half an inch below the overflow pipe topwater lineabout 3 inabout 1/2 in12345
Where water leaks out of a toilet tankSimple drawing, not to scale

Why a toilet keeps running

A toilet that runs, or refills by itself every few minutes or hours, is losing water one of two ways:

Over the top
The fill valve does not shut off, so water rises until it spills into the overflow pipe. Fix the fill valve.
Out the bottom
The flapper or canister seal lets water seep into the bowl, the tank level drops, and the fill valve turns on to top it up. Fluidmaster calls this ghost flushing. Fix the flapper or seal.

EPA says worn flappers are among the most common household leaks, and that a worn flapper can silently leak thousands of gallons a year.

Find the leak in four checks

  1. Lift the lid and watch the overflow pipe

    Flush and watch the tank refill. If water keeps pouring into the top of the overflow pipe after the tank is full, the fill valve is not shutting off or the water level is set too high. Fluidmaster's fix: lower the level so the water stops about 1/2 inch below the top of the overflow pipe, then flush debris from the valve, then replace it. Fill valve guide.

  2. Check the refill tube

    The small tube from the fill valve should be clipped above the overflow pipe opening. If it is pushed down into the pipe below the water line, it can siphon the tank and cause ghost flushing. Pull it out and clip it to the outside of the pipe.

  3. Run the dye test

    EPA's test: put a few drops of food coloring in the tank, do not flush, and wait 10 minutes. Color in the bowl means water is leaking past the flapper or canister seal. Flush afterward so the dye does not stain.

  4. Mark the water line to find where it leaks

    Fluidmaster's water test: with the tank full, close the stop valve, do not flush, and mark the water level. Wait 30 minutes, mark again, and keep waiting until it stops dropping. Where it stops tells you the leak point:

    • At the lip of the flapper: the flapper is worn or the seat is damaged.
    • All the way to the tank bottom: the flush valve gasket under the tank is worn, a tank-off repair.
    • Only 1/4 to 1/2 inch down, then stops: the refill tube is in the overflow pipe, or the overflow pipe is cracked.

Safety: Use the stop valve behind the toilet only if it turns smoothly. If it is stiff or starts dripping at the stem, close the house main instead.

Which part is in your tank

Hinged rubber flapper, about 3 in across

2-inch flapper: Fluidmaster 502, Korky 100BP.

Larger flapper, about 4 in across

3-inch flapper: Fluidmaster 5403, Korky 3060BP.

Tall cylinder, no flapper (Kohler)

Canister seal GP1059291.

Wide 4-inch valve on a guide rod

American Standard Champion 4 seal kit.

Water spills into the overflow pipe

Fill valve: Fluidmaster 400A or 400H.

Stop and call a plumber if

  • The stop valve will not close or leaks once moved.
  • Water is on the floor around the base of the toilet, or the floor is soft: the wax ring or flange has failed.
  • The level drains all the way to the bottom of the tank, or water drips from the tank bolts. Both mean taking the tank off.
  • The tank or bowl is cracked.
  • The supply line is corroded, kinked or bulging.