Why a toilet keeps running

The most common reason is a worn flapper that no longer seals properly, so water keeps leaking from the tank into the bowl and the tank keeps refilling. Other common causes include a faulty fill valve, a chain that is too short or too long, float problems, and buildup or misalignment inside the tank.

Quick checks

  • Lift the tank lid and look at the flapper; if it’s warped, cracked, or not seating flat, it likely needs adjustment or replacement.
  • Check the chain connection; if the chain is snagged, too tight, or too loose, the flapper may not close fully.
  • Watch the water level; if it rises too high and goes into the overflow tube, the fill valve or float is probably the issue.
  • Look for mineral buildup or other obstructions that stop parts from sealing correctly.

What to do

  1. Turn off the water supply to the toilet.
  2. Open the tank and inspect the flapper, chain, float, and fill valve.
  3. Adjust the chain or float if they’re mis-set.
  4. Replace the flapper if it looks worn or damaged.
  5. If the fill valve is faulty or the toilet still runs, a plumber may be needed.

Why it matters

A running toilet wastes water and can raise your bill noticeably over time. In many cases, it’s a simple fix, but if the problem keeps coming back, the issue may be deeper than a basic adjustment.

TL;DR

Most running toilets are caused by a bad flapper, a chain problem, or a faulty fill valve. Start with the tank lid, check those parts, and replace the flapper first if it looks worn.