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Toilet keeps running: what to check and what to buy

A running toilet is almost always one of three parts inside the tank, and the cheapest one is the most common culprit. Take the tank lid off and check in this order.

Before you start: To replace a part, turn off the shutoff valve behind the toilet and flush to empty the tank first.

What to check first

  1. The flapper

    Push down on the rubber flapper at the bottom of the tank. If the running stops, the flapper is not sealing because it is warped, stiff or coated in mineral buildup. This is the most common cause and the cheapest fix.

  2. The flapper chain

    A chain that is too short holds the flapper open, and one that is too long can get caught under it. Leave about half an inch of slack.

  3. The water level

    If water is spilling into the overflow tube, the fill level is set too high. Lower the float until the water stops about an inch below the top of the tube.

  4. The fill valve

    If the water still will not shut off, or the valve hisses and refills on its own, replace the fill valve.

  5. The flush valve seat

    If a new flapper still leaks, the seat it rests on may be pitted or cracked. Replacing the whole flush valve means taking the tank off the bowl.

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Ask Danny turns this job into a one-trip parts list for Home Depot and Lowe's, with aisle numbers and price estimates. Free, and no account needed.

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Parts you may need

  • Toilet flapperMatch the drain opening, usually 2 or 3 inches. Bring the old one to compare.
  • Toilet fill valveAdjustable universal models fit most toilets.
  • Flapper chainUsually included with a new flapper.
  • Flush valve kitOnly if the valve seat itself is damaged.

Tools

  • Sponge and towel
  • Adjustable wrench
  • Small bucket

Call a licensed pro if

  • The tank or bowl is cracked
  • The shutoff valve will not turn, or leaks when you turn it
  • Water is leaking onto the floor around the base

General guidance, not professional advice. Parts differ by brand and model, so check yours before buying. Aisle numbers and prices in the app are estimates. How Ask Danny uses AI. Updated September 16, 2026.

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