How do I fix a running toilet?
Diagnose the Problem
Remove the tank lid and listen. If water is flowing into the bowl, the flapper likely isn't sealing. If water is hissing into the tank, the fill valve or float may be misadjusted. Food coloring in the tank can help: add a few drops, wait 10 minutes, and see if color appears in the bowl—that means the flapper is leaking.
Turn off the water supply valve behind the toilet and flush to empty the tank. Inspect the flapper for warping, mineral buildup, or a worn chain. Check the fill valve for debris or a stuck float.
- Use food coloring to test for flapper leaks.
- Turn off water and flush before repairs.
- Inspect flapper, chain, and fill valve.
- Check the float height and adjust if needed.
Make the Repair
If the flapper is the issue, unhook the chain and slide the flapper off its pegs. Take it to a hardware store to match the size and shape. Install the new flapper, reattach the chain with about 1/2 inch of slack, and turn the water back on.
If the fill valve is faulty, you can often replace just the valve cap or the entire fill valve. A universal fill valve kit costs $10–$20 and comes with instructions. Adjust the float so the water level is about 1 inch below the overflow tube. Test by flushing and watching for leaks.
- Replace flapper if it's warped or dirty.
- Adjust chain length to allow full closure.
- Replace fill valve if it won't shut off.
- Set water level 1 inch below overflow tube.
Common mistakes
- Overtightening the flapper chain, which prevents it from sealing.
- Ignoring a running toilet—it can waste hundreds of gallons per day.
- Using the wrong size flapper, which won't seal properly.
