How to Fix a Running Toilet

September 5, 2026

Stop a toilet that runs constantly by checking the flapper, the chain, the float height, and the fill valve, in that order, with parts costing a few dollars.

Applies to: ordinary household fixtures and materials. Last checked September 5, 2026. Suggest an edit

The toilet keeps running, or turns itself on and off long after flushing. It is almost always one of four parts inside the tank, all of which cost a few dollars at a hardware store and need nothing more than a screwdriver.

Lift the tank lid and watch a flush

Set the lid somewhere it cannot fall. Flush and watch. The tank should refill and stop with the water about 1 inch below the top of the overflow tube, the open vertical pipe in the middle. If water keeps pouring into the overflow tube, or trickling into the bowl, keep going.

Press the flapper down

The flapper is the rubber disc at the bottom of the tank that lifts when you flush. Press it down with a finger. If the running stops, the flapper is worn or warped and no longer seals. To replace it, turn off the supply valve behind the toilet, flush to empty the tank, unhook the old flapper from the two pegs on the overflow tube and from the chain, and hook on the new one. Turn the water back on.

Check the chain slack

The chain from the flush lever to the flapper needs about half an inch of slack. Too tight and the flapper cannot seat; too loose and the chain gets caught under it. Move the clip up or down a link or two.

Set the water level

If water runs into the overflow tube, the float is set too high. On a fill valve with a float cup that rides up and down the valve stem, turn the adjustment screw or pinch the clip and slide the cup down. On an older ball float on an arm, turn the screw at the top of the valve, or bend the arm slightly downward. Flush and check that the water stops about 1 inch below the top of the overflow tube.

Replace the fill valve if it hisses

A fill valve that hisses constantly or refills in fits and starts has worn out. Turn off the supply, flush, sponge out the remaining water, unscrew the supply line and the nut under the tank, lift the old valve out, and install a new one at the height marked on the package. Universal fill valves fit nearly every toilet.

The cost of leaving it. A running toilet can waste hundreds of gallons a day, and it shows up on the next water bill.