A running toilet can waste hundreds of gallons per day and spike your water bill. Most causes are inexpensive wear parts inside the tank—not the bowl itself. With the water supply on, remove the tank lid and watch what happens after a flush.
Quick diagnosis: what you see in the tank
- Water spilling into the overflow tube: Fill valve set too high or failing to shut off.
- Flapper not sealing: Water leaks from tank to bowl, triggering endless refills.
- Chain too tight or too loose: Prevents the flapper from closing fully.
- Intermittent ghost flushing: Often a slow flapper leak or flush valve seal issue.
Step-by-step fixes
- Adjust the fill valve. Lower the float or turn the adjustment screw so water stops about one inch below the overflow tube.
- Test the flapper. Press down on it with a stick. If the running stops, replace the flapper—it should match your valve size and brand when possible.
- Check the chain. Leave slight slack when the flapper is closed; too much tension keeps it open slightly.
- Inspect the flush valve seat. Mineral buildup or cracks prevent sealing. Clean gently or replace the flush valve assembly if worn.
- Replace the fill valve if it hums, sputters, or never fully shuts off after adjustment.
Parts that fix most running toilets
- Universal flapper ($5–$15)
- Fill valve kit ($15–$30)
- Complete tank rebuild kit ($25–$45) for older toilets with multiple worn parts
Turn off the supply valve at the wall, flush to empty the tank, swap the part, and turn water back on slowly while checking for leaks.
When to call a plumber
- Running continues after replacing flapper and fill valve.
- Cracks in the tank or bowl, or water on the floor around the base.
- Supply line or shut-off valve is corroded and will not stop flow safely.
- Older low-flow or dual-flush models need manufacturer-specific parts.
Final takeaway
Most running toilets are fixed in under an hour with a flapper or fill valve swap. Do the food-coloring test if you are unsure: add dye to the tank; color in the bowl without flushing confirms a flapper leak. If simple parts do not solve it, a plumber can rule out hidden leaks at the wax ring or supply connection.