A Toilet That Runs

A tank has one job: hold a measured volume of water and release all of it at once. Two parts control that. The flapper is the rubber seal at the bottom that lifts to flush and drops to seal. The fill valve is the column at the side that refills the tank and shuts off at a set level.

A running toilet is one of them failing, and which one it is decides whether the noise is continuous or intermittent.

If the sound never stops, water is leaving the tank as fast as the fill valve replaces it. That is the flapper not sealing — warped, coated in mineral scale, or held fractionally open by a chain that is too short.

EPA describes exactly this failure: a worn flapper can cause a toilet to flush on its own or silently leak thousands of gallons a year. Silently is the important word. A flapper leak does not have to make a sound to be running.

Source: US EPA WaterSense, Fix a Leak Week.

A toilet that hisses for twenty seconds every ten minutes and then stops is doing the same thing at a lower rate. The level falls below the fill valve's threshold, the valve tops it up, and the cycle repeats. This is the version people live with for years because it is not annoying enough to chase.

EPA publishes a test that needs nothing but food coloring: put a few drops in the tank, do not flush, and look in the bowl after ten minutes. Color in the bowl means the flapper is leaking.

If the dye stays in the tank and the toilet is still running, the fill valve is overfilling — water is going down the overflow tube instead of past the flapper, which is a different part and a different repair.

EPA reports that household leaks waste nearly 1 trillion gallons annually across the country, that the average household loses more than 9,300 gallons a year to them, and that nine percent of homes have leaks wasting 50 gallons or more a day.

A toilet is the likeliest single source of that, because it is the only fixture in the house that can leak continuously into a drain where nobody ever sees it.

Both parts are replaceable and neither is a major job. The reason to call someone is if the flapper has been replaced and it still leaks — that usually means the seat it closes onto is pitted or scaled, which is a different repair, and on an old fixture it is the point where replacing the toilet starts to make more sense than repairing it again.