Toilet Keeps Refilling on Its Own: Fill Valve or Flapper?

Homeowners describe it in a few ways: "my toilet runs for two seconds every ten minutes," "it fills all night," or "I replaced the fill valve and the flapper and it still runs." All of them come back to the same two parts inside the tank — the flapper, which holds water in the tank, and the fill valve, which refills it. If you only want to confirm a leak first, our toilet dye test guide shows how. This page is about working out which part is at fault.

The overflow tube test

Take the tank lid off and watch the water level after the tank refills.

• Water is spilling into the overflow tube (the open pipe in the middle of the tank): the fill valve isn't shutting off. Either the float is set too high or the valve itself is worn or has debris in it.
• Water stays below the top of the overflow tube, but the toilet still refills every so often: water is leaking past the flapper into the bowl, the level drops, and the fill valve tops it back up. That on-off cycling is the classic "phantom flush."

When it's the flapper

• Chain too short or tangled, holding the flapper slightly open. Leave a little slack.
• A warped or hardened flapper. Rubber ages, especially with chlorinated or hard water — see hard water and your plumbing.
• A rough or chipped flush valve seat — the ring the flapper sits on. A new flapper can't seal on a damaged seat, which is why some people replace the flapper and still have a leak. Seat repair kits exist, but sometimes the flush valve itself needs replacing.

When it's the fill valve

• Float set too high. Lower it until the water stops about an inch below the top of the overflow tube.
• Debris in the valve. Sediment from a recent water shutoff or street work can lodge in the valve seal, so it never fully closes. Flushing the valve or replacing the seal often fixes it.
• A worn valve. Fill valves don't last forever; if adjusting and cleaning don't help, replacement is usually the answer.

"I replaced both and it still runs"

That usually means one of three things: the new flapper isn't the right size or style for the flush valve, the flush valve seat is damaged, or the water level is set too high on the new fill valve. Less often, a leak between the tank and bowl (at the tank bolts or the gasket) is the real issue — look for water on the floor or dripping from the bolts.

Why it's worth fixing soon

A toilet that runs constantly can waste a large amount of water before anyone notices — it's one of the most common reasons behind a sudden high water bill. If you need to stop it right now, turn the small supply valve behind the toilet clockwise. If that valve won't close or starts to drip, see where your shut-off valves are.

When to call a plumber

Call if the supply valve is stuck or leaking, if water is coming from the tank bolts or base, if the flush valve needs replacing and the tank has to come off, or if you've replaced parts and it still won't stop. In Torrance, call Rush Plumber at (209) 860-5004 or see our plumbing services.

Reviewed by the Rush Plumber team — licensed, insured plumbers serving Torrance, CA and the South Bay, 3610 Torrance Blvd, Torrance, CA 90503. Call (209) 860-5004, 24/7.