How to Fix a Running Toilet: Easy DIY Fix

A running toilet wastes up to 200 gallons of water per day — costing $50–$100 per month extra on your water bill. Fixing it typically takes 30 minutes and costs under $20.

Why Is Your Toilet Running?

The three most common causes are: a faulty flapper, a misadjusted float, or a defective fill valve.

Diagnosing the Problem

1. Remove the tank lid and set it safely aside
2. Add a few drops of food coloring to the tank
3. Wait 15 minutes — if color appears in the bowl without flushing, you have a flapper leak
4. If the water level is above the overflow tube, the fill valve or float needs adjustment

Fix #1: Replace the Flapper (Most Common Fix)

Turn off the water supply valve. Flush to empty the tank. Unhook the old flapper from the pegs on the overflow tube and disconnect the chain from the flush handle arm. Snap in the new flapper (available for $5–$10 at hardware stores), attach the chain with 1/2 inch of slack, and turn water back on.

Fix #2: Adjust the Float

The water level should be about 1 inch below the top of the overflow tube. On a ball float, bend the arm down slightly. On a cup float, squeeze the clips and slide the float down. Flush and check the water level.

Fix #3: Replace the Fill Valve

If the toilet keeps running after replacing the flapper and adjusting the float, the fill valve likely needs replacement. A universal fill valve (like Fluidmaster 400A) costs about $12 and is a straightforward swap — turn off water, flush, sponge out remaining water, unscrew the locknut under the tank, swap the valve, and reconnect.