Running Toilet Repair: Diagnose and Fix It in 15 Minutes

Flapper, fill valve, or chain — the three reasons toilets run nonstop and how to fix each one without flooding the bathroom.

A toilet that keeps running between flushes — or that randomly refills every 20 minutes — is the single most expensive ignored plumbing problem in the average home. A continuously-running toilet wastes 200+ gallons per day. The fix is almost always cheap and almost always one of three parts.

1. Flapper not sealing. The most common cause. The rubber flapper at the bottom of the tank has warped or hardened and water is bypassing it into the bowl. Symptom: the fill valve cycles on briefly every few minutes when nobody's used the toilet. Fix: replace the flapper. $8 part, 10 minutes. Match the brand — a Korky 2" universal fits 90% of post-1996 toilets, but Kohler Class Five and some Toto models need their specific flapper.

2. Fill valve stuck on. The fill valve at the top of the tank won't shut off because the float is sticking, the diaphragm is shot, or debris from Corona's hard water is fouling the seat. Symptom: water keeps trickling into the overflow tube even after the tank is full. Fix: replace the fill valve. A Fluidmaster 400H is $14 and a 20-minute swap.

3. Chain too short or too long. Chain too short = flapper can't seal flat. Chain too long = it gets sucked under the flapper. Symptom: intermittent running, often after a flush. Fix: adjust the chain so there's roughly 1/2" of slack with the flapper closed. Free, 60 seconds.

The 15-minute repair. Shut the angle stop behind the toilet. Flush to empty the tank. Sponge out the last inch of water. Disconnect the supply line. Unscrew the flapper or fill valve. Drop the new part in. Reconnect. Open the angle stop and confirm a clean fill and shutoff.

When to call. If the angle stop won't fully close, if the tank-to-bowl gasket is leaking (water on the floor between tank and bowl), or if the toilet is 25+ years old and parts are unobtainable, it's time for a service call or a replacement. (951) 582-2433 — typical flat-rate toilet rebuilds in Corona run $145–$240.

Keep reading: Leaky Faucet Repair in Corona Homes · The Complete Corona Plumbing Repair Guide.