Toilet Keeps Running: How to Fix a Running Toilet

Common Symptoms

• Toilet hisses or runs continuously after flushing
• Toilet turns on and off periodically on its own ('phantom flush')
• Water runs into the bowl long after the tank fills
• Tank never fully fills and keeps running
• Water bill is higher than usual

Most Likely Causes

1. 1

   Worn Flapper Valve (Most Common)

   The flapper is the rubber valve at the bottom of the tank that seals against the flush valve seat. Over time it warps, deteriorates, or gets coated with mineral buildup, preventing a proper seal. Water slowly leaks into the bowl, and the fill valve keeps running to compensate. This is the most common running toilet cause.

2. 2

   Float Set Too High

   If the water level in the tank rises above the overflow tube, water continuously drains into the bowl and the fill valve keeps refilling. Adjusting the float down 1/2 inch below the top of the overflow tube immediately stops this.

3. 3

   Faulty or Worn Fill Valve

   The fill valve refills the tank after each flush. When the fill valve wears out, it may not shut off completely — letting a small trickle of water continuously flow into the tank and out through the overflow. A complete fill valve replacement costs about $12.

4. 4

   Flush Chain Too Short or Tangled

   If the chain connecting the flush handle to the flapper is too short, kinked, or tangled, it can hold the flapper slightly open all the time — causing a constant slow leak into the bowl. Adjust the chain to have 1/2 inch of slack.

Quick DIY Checks

1. 1Remove the tank lid and observe: if water is flowing over the top of the overflow tube, the float is set too high. Adjust the float arm or turn the adjustment screw on the fill valve until the water level is 1/2 inch below the top of the overflow tube.
2. 2Test the flapper: add a few drops of food coloring to the tank water. Wait 15–20 minutes without flushing. If colored water appears in the bowl, the flapper is leaking and needs replacement.
3. 3Check the chain: it should have about 1/2 inch of slack. If it's too short (holds flapper open) or too long (gets caught under the flapper), adjust the clip position on the flush handle arm.

Repair vs Replace

Recommended Tools & Parts

• Universal Toilet Flapper

  Universal rubber flapper that fits most standard toilets. Replace when leaking or running won't stop.

  $5–$10

  Buy on Amazon →

• Fluidmaster 400A Fill Valve

  The most popular toilet fill valve replacement. Adjustable height fits most tanks and installs in 15 minutes.

  $10–$15

  Buy on Amazon →

• Toilet Tank Repair Kit

  Complete repair kit including flapper, fill valve, and flush valve. Fixes running, phantom flush, and slow fill.

  $15–$25

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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