Symptoms
- Toilet runs on and off or continuously
- Hissing sound from the tank
- Water level in tank drops faster than normal
- Flapper looks warped, discolored, or coated in grime
Likely causes
- CommonWorn or warped rubber flapperRubber degrades over years, especially with in-tank chlorine cleaning tablets, and stops sealing flat.
- CommonMineral or grime buildup on the seatDeposits on the valve seat prevent full contact even with a good flapper.
- PossibleMisaligned flapper or chain interferenceThe flapper sits off-center or the chain catches, holding it slightly open.
What to do
- Turn off the water supply and flush to drain most of the tank.
- Unhook the flapper from its mounting pegs or ring and inspect it for warping, cracking, or grime.
- Wipe the valve seat clean with a cloth and a little vinegar if there's visible buildup.
- Install a new universal flapper matching your toilet's flush valve size (usually 2 inch or 3 inch).
- Adjust the chain to have a small amount of slack once the new flapper is hooked up.
- Turn the water back on, let the tank fill, and check for leaks with a dye test.
Tools and parts
- Gloves
- Vinegar
- Cloth
Universal toilet flapperSearch: “universal toilet tank flapper 2 inch or 3 inch”
When to call a pro
A plumber isn't usually needed for a flapper swap, but call one if the valve seat itself looks damaged or corroded.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.