How to Fix a Running Toilet (Flapper, Fill Valve, and Chain)

A running toilet almost always comes down to one of three things: the flapper, the chain, or the fill valve (float). You can diagnose it in two minutes by looking inside the tank.

In this guide

1. Step 1: Find the cause
2. Fix 1: Adjust the chain
3. Fix 2: Lower the float
4. Fix 3: Clean or replace the flapper
5. Fix 4: Replace the fill valve
6. When to call a plumber

Step 1: Find the cause

Lift the tank lid and set it somewhere safe. It’s heavy and breaks easily.

• Water running into the overflow tube (the open pipe in the middle): the water level is set too high, or the fill valve isn’t shutting off.
• No water in the overflow tube, but the toilet refills on its own every so often: water is leaking past the flapper into the bowl.
• The handle stays down or the flapper won’t close: the chain is tangled or too short.

Dye test: put a few drops of food coloring in the tank and don’t flush for 20 minutes. If color shows up in the bowl, the flapper is leaking.

Fix 1: Adjust the chain

The chain should have about ½ inch of slack when the flapper is closed. Too tight and the flapper can’t seal. Too loose and it can get caught under the flapper. Move the clip to a different link and test.

Fix 2: Lower the float

The water should stop about 1 inch below the top of the overflow tube.

• Cylinder float (slides on the fill valve): squeeze the clip or turn the adjustment screw to lower it.
• Ball float (on a metal arm): turn the screw on top of the valve, or gently bend the arm down.

Fix 3: Clean or replace the flapper

1. Turn off the water at the valve behind the toilet and flush to empty the tank.
2. Unhook the flapper from the overflow tube and the chain.
3. Wipe the flapper and the drain seat with a cloth to remove buildup. A warped, stiff, or slimy flapper should be replaced.
4. Take the old flapper to the hardware store to match the size (most are 2 or 3 inches), or buy a universal one.
5. Hook it on, attach the chain, turn the water on, and test.

Fix 4: Replace the fill valve

If the valve keeps hissing after you adjust the float, replace it. Universal kits come with instructions:

1. Turn off the water, flush, and sponge out the tank.
2. Put a towel down. Disconnect the supply line under the tank.
3. Unscrew the plastic locknut under the tank and lift out the old valve.
4. Install the new valve, set it to the height in the kit’s instructions, and hand-tighten the locknut plus a quarter turn.
5. Reconnect the supply line, clip the refill tube to the overflow tube, turn the water on, and check for leaks.

When to call a plumber

Call a plumber if the tank leaks onto the floor, the shutoff valve won’t turn, or the tank or bowl is cracked.