How to Troubleshoot a Running Toilet

A running toilet is usually caused by water escaping past the flapper or by the fill system failing to shut off at the correct level. Watching what happens inside the tank often tells you which part is responsible.

Tools you will probably need

• flashlight
• sponge or towel
• basic pliers if a part requires them

Materials

• possibly a flapper, fill valve, or chain adjustment

Project steps

1. Remove the tank lid and observe whether water is flowing into the overflow tube or leaking past the flapper.
2. Check that the flapper closes fully and that the chain is not holding it open.
3. Confirm the tank water level is below the top of the overflow tube.
4. Adjust or replace the faulty tank component according to its instructions, then test multiple flushes.

Common mistakes

• Replacing random parts before observing the failure
• Ignoring a shutoff valve that will not close
• Overtightening plastic tank fittings

When to call someone

Call a plumber if water is leaking outside the tank, the shutoff valve is seized, the toilet rocks, or tank adjustments do not stop the problem.

Project costs and times are rough planning estimates. Product instructions, local codes, home construction, and actual conditions take priority.