How to fix a running toilet

For anyone hearing a nonstop hiss from the bathroom, this restores a quiet seal and stops the wasted water.

IJR · Sep 26, 2026 · 2 min read

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A running toilet keeps adding water because the flapper is not seating flat or the tank level sits too high. Seating that seal and setting the level one inch below the overflow tube ends the flow.

Have a towel, a sponge, pliers, and a matching replacement flapper ready beside the tank.

1: LISTEN beside the open tank to pin the sound to flapper or fill valve. — **1: LISTEN** beside the open tank to pin the sound to flapper or fill valve.

Lift the lid and set it safely on the floor. A steady trickle into the overflow tube means the flapper is leaking; silence after the fill cycle ends points to the fill valve instead.

2: SHUT the wall supply valve fully clockwise until it stops turning. — **2: SHUT** the wall supply valve fully clockwise until it stops turning.

Kneel and turn the valve low on the left side all the way; a partial turn still lets water creep in. Blot any drips with the towel so the floor stays dry.

3: FLUSH and hold the handle down until the tank empties. — **3: FLUSH** and hold the handle down until the tank empties.

Water drops out through the flush valve. Sponge up the last inch so the flapper area stays dry while you work.

4: LIFT the flapper by its side ears and inspect the rubber face. — **4: LIFT** the flapper by its side ears and inspect the rubber face.

Check for warps, cracks, or white mineral crust. A smooth even face will seat; if it is stiff or torn, unhook the chain and ears and set the old flapper aside.

5: CLIP the new flapper onto the overflow ears and set half an inch of chain slack. — **5: CLIP** the new flapper onto the overflow ears and set half an inch of chain slack.

Snap the side ears onto the posts, then hook the chain through a middle link so the flapper can drop flat. Too little slack holds it open; too much lets it drift sideways.

6: RAISE or lower the float until water stops one inch below the overflow rim. — **6: RAISE** or lower the float until water stops one inch below the overflow rim.

Open the supply valve a quarter turn at a time and watch the rising line. Turn the fill-valve screw or slide the float cup so the water sits one inch under the top of the overflow tube.

7: TEST with two full flushes and a two-minute watch on the water line. — **7: TEST** with two full flushes and a two-minute watch on the water line.

Let the tank refill, mark the level lightly with a pencil, then wait. No drop in the mark and no hiss means the seal is holding.

The most common mistake

The chain is left too tight so the flapper never drops shut. Add half an inch of slack so it falls flat on the seat.

Pro tip

Wipe a thin film of plumber’s silicone grease on the new flapper edge so it seats cleanly past mineral film.

Say it every time

Listen shut flush lift clip set test

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The most common mistake

Pro tip

Say it every time

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