Symptoms
- Water sound never stops after flushing
- Tank refills over and over
- Water bill has jumped
- Faint hissing from the tank
Likely causes
- CommonWorn or misaligned flapperThe rubber flapper at the bottom of the tank no longer seals, letting water leak into the bowl.
- CommonFill valve not shutting off fullyThe fill valve keeps trickling water even after the tank should be full.
- PossibleFloat set too highWater reaches the overflow tube and drains continuously before the valve can shut off.
- PossibleChain too short or tangledA short chain holds the flapper slightly open; a tangled one can catch and prevent a full seal.
- Less commonCracked overflow tubeWater escapes through a crack instead of staying in the tank.
What to do
- Take the tank lid off and listen/look at the water level relative to the overflow tube.
- If water is at or above the top of the overflow tube, the float is set too high or the fill valve is faulty.
- Watch the flapper right after a flush; if it doesn't drop flat and seal, that's your leak.
- Check the chain: it should have a small amount of slack, not be taut and not be tangled around the flapper.
- Do a dye test: add a few drops of food coloring to the tank and wait 10 minutes without flushing; color in the bowl means the flapper is leaking.
- Replace a worn flapper with a matching universal one, or adjust/replace the fill valve if it won't shut off.
- Lower the float slightly if water sits above the overflow tube, then re-test.
Tools and parts
- Gloves
- Old towel
- Replacement flapper (if needed)
Universal toilet flapperSearch: “universal toilet tank flapper replacement”
When to call a pro
Call a plumber if replacing the flapper and adjusting the float doesn't stop the running, since the fill valve or tank may need replacing.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.