How to Fix a Running Toilet

6 steps 30 min Beginner From $22

A running toilet wastes ~200 gallons a day. Almost every running toilet is one of three problems: a bad flapper, a misadjusted fill valve, or a chain that's too tight. The fix is $15 and 30 minutes — and the parts have universal designs that fit almost any toilet.

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Step-by-Step Instructions

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Step 1: Diagnose the cause

Open the tank lid and watch. Water still trickling into the bowl from a leaky flapper? Water flowing into the overflow tube? Fill valve refilling endlessly? Each has a different fix.

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Water leaking into bowl — flapper problem

The flapper at the bottom doesn't seal. Drop a few drops of food coloring in tank; if it appears in the bowl within 15 min, it's the flapper.

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Water in overflow tube — fill valve set too high

Tube in middle of tank is overflowing into the bowl. Bend the float arm down (older style) or twist the float adjustment (modern).

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Fill valve constantly running — bad fill valve

Fill valve never shuts off. Replace it entirely — they wear out in 5-10 years.

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Step 2: Shut off the water

Valve at the base of the toilet (left side wall). Turn clockwise. Flush to drain tank. You'll have a few inches of residual water in the bottom — sponge it out for cleaner work.

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Close the wall valve, flush to drain

Standard. Flush once after the valve closes — tank drains.

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Sponge out residual water

After flushing, ~1 inch of water remains. Sponge into a bucket so you can work dry.

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Step 3: Replace the flapper (most common fix)

Universal flappers fit almost every toilet. Unhook from the chain, slip the rubber ears off the overflow tube, slide on the new one, hook the chain. 5 minutes.

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Korky 2003BP universal flapper

Fits 99% of US toilets. Korky is the OEM for many brands. ~$8-12.

$10 View Details
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Fluidmaster 502P21 flapper

Slightly cheaper alternative, similar fit. ~$5-8.

$7 View Details
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Brand-specific flapper (Kohler, Toto)

If your toilet is Kohler or Toto, OEM flappers fit better. Search the brand + 'flapper' + model. ~$10-15.

$12 View Details
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4

Step 4: Adjust or replace the fill valve

Modern Fluidmaster 400A fits almost everything. Disconnect the supply line, unscrew the locknut under the tank, pull the old valve up, drop the new one in, reverse. Adjust water level by twisting the float housing.

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Fluidmaster 400A universal fill valve

The default replacement. Adjustable height, fits 99% of tanks. ~$11-15.

$12 View Details
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Korky 528 Quietfill (quieter alternative)

Quieter refill. Slightly more expensive. ~$15-22.

$18 View Details
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Adjust without replacing (older style)

If the fill valve has a horizontal arm with a float ball, just bend the arm down — lowers water level, stops overflow. Free.

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5

Step 5: Fix the chain length

Chain too tight: flapper can't seal flat — running. Chain too loose: handle won't lift flapper — won't flush. Adjust by hooking the chain at different hole on the flush lever — 1/2 inch of slack is the sweet spot.

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1/2 inch chain slack (rule of thumb)

Move the chain hook to a different hole until you have about 1/2 inch of slack when the flapper is closed.

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Replace bent or kinked chain

Cheap. Fluidmaster Universal Lift Chain. ~$3.

$3 View Details
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6

Step 6: Turn water back on and test

Open the wall valve. Let tank fill. Flush 2-3 times. Watch the cycle: tank fills, fill valve closes, water doesn't leak into bowl. Check overflow tube isn't being filled.

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Flush 2-3 times and watch the cycle

Verify water level stops below overflow tube (about 1" below the top).

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Listen for fill valve cycling on/off

After the tank fills, the valve should stop. If it kicks back on every minute or two, the flapper is still leaking — replace the flapper.

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