How to Fix a Running Toilet in 10 Minutes

A running toilet wastes 200 gallons of water per day (about $50 to $100 per month on your water bill) and produces that constant, maddening trickle sound. The cause is almost always one of three cheap parts inside the tank. You do not need a plumber for this repair.

Diagnose the Problem: The Food Coloring Test

Remove the toilet tank lid (it lifts straight off). Drop 5 to 10 drops of food coloring into the tank water. Wait 10 minutes without flushing. If colored water appears in the bowl, the flapper valve is leaking, which is the cause in about 70% of running toilets.

If the water level in the tank is above the overflow tube (the tall vertical pipe in the center of the tank) and water is flowing into the overflow tube, the fill valve needs adjustment or replacement.

Fix 1: Replace the Flapper Valve (70% of Cases)

The flapper is the rubber disc at the bottom of the tank that seals the flush valve opening. After 3 to 5 years, the rubber warps, cracks, or develops mineral deposits that prevent a watertight seal. Water slowly leaks past the flapper into the bowl, and the fill valve periodically turns on to refill the tank.

Turn off the water supply valve (the knob on the wall behind the toilet, turn clockwise). Flush the toilet to empty the tank. Unhook the old flapper from the two pegs on the overflow tube and disconnect the chain from the flush lever. Take the old flapper to a hardware store to match the size (universal flappers fit 90% of toilets and cost $3 to $8).

Hook the new flapper onto the overflow tube pegs, connect the chain to the flush lever with about half an inch of slack, and turn the water supply back on. The chain should have just enough slack that the flapper seats fully when closed, but not so much that it gets caught under the flapper during flushing.

Fix 2: Adjust the Fill Valve (25% of Cases)

If the water level in the tank is above the overflow tube, the fill valve is set too high. Water continuously runs into the overflow tube and down into the bowl. Locate the fill valve (the tall assembly on the left side of the tank). Most modern fill valves have an adjustment screw or clip on the float arm or float column.

For float cup valves (the most common modern type), squeeze the adjustment clip on the float column and slide the float downward about half an inch. This lowers the water level set point so the valve shuts off before water reaches the overflow tube. Flush and check that the water level stops about 1 inch below the top of the overflow tube.

For older ball-float valves (the kind with a rubber ball on the end of a horizontal arm), bend the metal arm downward slightly. This causes the ball to reach its shutoff position at a lower water level.

Fix 3: Replace the Fill Valve (5% of Cases)

If adjusting the fill valve does not stop the running, the valve itself is worn out and does not shut off reliably. Replacement fill valves cost $7 to $15 at hardware stores and take 15 to 20 minutes to install.

Turn off the water supply. Flush to empty the tank. Disconnect the water supply line from the bottom of the tank (have a towel ready for residual water). Unscrew the locknut on the outside bottom of the tank that holds the old fill valve. Remove the old valve and insert the new one, adjusting the height to match your overflow tube. Tighten the locknut hand-tight plus a quarter turn with pliers. Reconnect the water supply, turn it on, and adjust the water level.

The Handle and Chain Check

If the toilet runs intermittently (not constantly), the flush lever chain may be too short, holding the flapper slightly open, or the chain may be tangled and preventing the flapper from seating properly. Flush the toilet and watch the flapper close. It should drop onto the valve seat completely and seal immediately after the tank empties. Adjust the chain length if it does not.

Bottom Line

A running toilet is almost always a $5 to $15 fix. Replace the flapper if water leaks from tank to bowl (the food coloring test). Adjust the fill valve float downward if the water level is above the overflow tube. These two fixes handle 95% of running toilets in under 10 minutes.