If a toilet keeps running, check whether water is flowing into the overflow tube or leaking past the flapper. Those two paths cover most running toilet problems.

Quick checks

  • Remove the tank lid carefully.
  • See whether the water level is too high and spilling into the overflow tube.
  • Check whether the flapper is sealing after the flush.
  • Look for a chain that is too tight, tangled, or stuck under the flapper.
  • Turn the shutoff valve off if water is wasting fast or the toilet may overflow.

If water is going into the overflow tube

The fill valve may be set too high, stuck, dirty, or failing. The water level should stop below the top of the overflow tube. If it keeps rising, adjust or clean the fill valve according to the part instructions. Replace it if cleaning and adjustment don't hold.

If water leaks past the flapper

Turn the water supply off after the tank fills and mark the water level. If the level drops, the flapper or flush valve seal is a likely suspect. Fluidmaster identifies flapper leakage as a common running toilet cause.

Small things that cause big annoyance

  • A flapper chain with no slack.
  • A flapper warped by age or cleaners.
  • Debris on the flush valve seat.
  • A float rubbing against the tank wall.
  • A fill valve that never shuts off cleanly.

When to replace parts

Replace the flapper if it is warped, slimy, cracked, or doesn't seal after cleaning. Replace the fill valve if the water level keeps rising, the valve runs randomly, or adjustment doesn't hold.

When to call a plumber

Call a plumber if the shutoff valve won't turn, the toilet rocks, the tank is cracked, water appears on the floor, or you aren't comfortable working inside the tank.

Good maintenance rhythm

  • Monthly: lift the tank lid and listen. A toilet that refills on its own without a flush is wasting water.
  • Every 4 to 5 years: plan to replace the flapper. Rubber stiffens and stops sealing.
  • Every 5 to 7 years: plan to replace the fill valve. Most plastic fill valves wear out in that range.
  • After any flush that didn't shut off: check the flapper and chain first.
  • Ongoing: skip drop-in bleach tablets in the tank. They shorten flapper life and accelerate the next running toilet.
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