A toilet keeps running because water is leaking from the tank into the bowl or the tank never stops filling. The three most common causes are a worn or warped flapper, a float set too high so water spills into the overflow tube, and a failing fill valve.
How a toilet tank works
When you flush, the flapper lifts and the tank empties into the bowl. The flapper drops and seals the flush valve, and the fill valve refills the tank until the float reaches the set level and shuts it off. A running toilet means one of those steps isn’t finishing.
Cause 1: The flapper is leaking
Rubber flappers wear, warp and collect mineral deposits over time, so they stop sealing. Water trickles into the bowl, the tank level drops, and the fill valve turns on to top it up, sometimes with a periodic hiss known as “phantom flushing.”
Test: put a few drops of food coloring in the tank and wait 15 to 20 minutes without flushing. If color appears in the bowl, the flapper is leaking.
Fix: replace the flapper with one that matches the flush valve size, commonly 2 or 3 inches. Also check that the chain has a little slack, as too tight keeps it from sealing.
Cause 2: The water level is too high
If the float is set too high, water fills above the top of the overflow tube and spills into the bowl continuously.
Fix: adjust the float so the water stops about an inch below the top of the overflow tube, or at the line marked inside the tank.
Cause 3: The fill valve is failing
If the water level is correct and the flapper seals, but you still hear water running or the valve won’t shut off, the fill valve may be worn or clogged with debris.
Fix: replace the fill valve. It’s a common repair, but it requires shutting off the supply and disconnecting the supply line.
Other causes
- A cracked overflow tube or worn flush valve seat
- A refill tube pushed too far down the overflow tube, siphoning water
- High water pressure affecting the fill valve
Why fix it promptly?
A running toilet can waste a large amount of water day after day, and in many homes it’s the single biggest reason for an unexplained water bill increase. In a condo or a seasonal home, a toilet that runs while you’re away can waste water for weeks.
When to call a plumber
Call a plumber if the shut-off valve behind the toilet is stuck or leaking, if parts don’t solve the problem, if water is leaking at the base or the toilet rocks, or if the toilet is cracked. Our toilet repair and installation page covers what’s involved, and our guide to hidden water leaks explains how to confirm a leak with your meter.
Call (561) 794-0131 to connect with an independent Boca Raton plumbing contractor near you.
Frequently asked questions
Why does my toilet run every few minutes by itself?
That’s usually a leaking flapper letting water seep into the bowl, so the tank refills periodically. The food coloring test can confirm it.
Can a running toilet increase my water bill?
Yes. A continuously running toilet can waste a significant amount of water and noticeably raise your bill.
How do I stop a toilet from running temporarily?
Turn the shut-off valve behind the toilet clockwise until it stops. That stops refilling until you can fix it.
Should I replace the whole toilet if it keeps running?
Usually not. Flappers and fill valves are inexpensive parts. Replacement makes sense if the toilet is cracked, clogs frequently or parts are unavailable.