Toilet Keeps Running: Causes & Fixes

May 24, 2026 4 min read

Why your toilet keeps running

A toilet that runs constantly — or cycles on and off every few minutes — can waste up to 200 gallons of water a day. In Scottsdale's tiered water rates, that's a real number on your bill, fast. The good news: most causes are cheap to fix, and you can DIY several of them.

Here are the six most common causes, in the order a plumber checks them.

1. A worn or warped flapper

The rubber flapper at the bottom of the tank seals water in. Over time — especially in Scottsdale's hard, chlorinated water — it warps, curls, or gets coated in mineral buildup and stops sealing.

Fix: Shut off the angle stop, flush, replace the flapper ($5–$15). Match brand if possible — Korky, Fluidmaster, and Kohler all use slightly different shapes.

2. Chain too tight or too loose

A chain with no slack holds the flapper slightly open. A chain with too much slack catches under the flapper.

Fix: Adjust so there's about a half-inch of slack when the flapper is closed.

3. Fill valve set too high

If water trickles into the overflow tube nonstop, your fill valve is set above the overflow level.

Fix: Lower the float so water stops about 1 inch below the top of the overflow tube. Most modern Fluidmaster valves adjust by twisting the top.

4. Failed fill valve

Fill valves wear out — usually 5–10 years in Scottsdale's hard water. Symptoms: phantom flushes, hissing, water level that creeps up, or a valve that won't fully shut.

Fix: Replace the entire fill valve ($15–$25 for parts). DIY-friendly with a wrench and 20 minutes.

5. Mineral buildup on the flush valve seat

The plastic ring the flapper sits on collects calcium and chlorine residue, breaking the seal even with a brand-new flapper.

Fix: Shut off water, drain the tank, gently scrub the seat with a Scotch-Brite pad. Don't sand it.

6. Cracked overflow tube or flush valve

If you've replaced the flapper, the fill valve, and the seat is clean and it still runs, you likely have a hairline crack in the flush valve or overflow tube.

Fix: Replace the entire flush valve — or honestly, at this point, the smarter move is a new toilet. Once two or three components have failed, the rest are close behind.

When to just replace the toilet

The toilet is 20+ years old (uses 3.5+ gallons per flush)
You've replaced internals twice in 2 years
The porcelain is cracked or stained beyond cleaning
You're still using a pre-1994 high-flow model

A new 1.28 GPF toilet pays for itself in water savings in 3–5 years for a typical Scottsdale household.

Related services from Dominick Plumbing

Licensed in Arizona (ROC #350819). Call (623) 323-4538 for same-day toilet service.