How to Fix a Running Toilet: Safe Checks and Common Tank Repairs

Last updated: October 9, 2026

A toilet that keeps running usually has a problem inside the tank, such as a worn flapper, tangled chain, incorrect water level, or fill-valve issue. Start with a simple leak check. Shut off the supply valve only if it turns normally; do not force a stuck or corroded valve.

Check for a silent leak

EPA WaterSense recommends putting a few drops of food coloring or a dye tablet in the tank and waiting about 10 minutes without flushing. If color appears in the bowl, water is leaking past the flapper or flush-valve seal. Flush afterward so the dye does not stain the fixture. See EPA WaterSense home maintenance guidance.

Inspect the tank safely

1. Lift the tank lid carefully and set it on a stable surface.
2. Look for water continuously flowing into or over the overflow tube. The water level should follow the toilet manufacturer’s guidance.
3. Check whether the chain is tangled, too tight, or preventing the flapper from closing fully.
4. Observe whether the flapper lies flat over the flush opening and whether the handle returns freely.

Do not reach into the tank if you see damaged wiring, an unfamiliar powered component, or anything that makes the repair unsafe. Toilets vary; check the manufacturer’s instructions for the exact model.

Common fixes

• Tangled chain: Restore enough slack for the flapper to close while still lifting when the handle is pressed.
• Worn or mismatched flapper: Replace it with a part compatible with the toilet model. Mineral buildup or age can prevent a good seal.
• Water level or fill valve: If water continues into the overflow tube, adjust the float only as the manufacturer directs. If the valve will not stop filling, replacement or a plumber may be needed.
• Persistent leak after replacing the flapper: The flush-valve seat, fill valve, or another tank component may be the cause. Avoid repeated part swaps without diagnosis.

EPA says toilet flappers wear out and recommends checking them periodically; it also advises contacting a local plumber when the problem continues or the cause is unclear. See EPA’s Fix a Leak Week resources.

When to call a plumber

Get help if the shutoff valve is stuck, the toilet rocks or leaks at the floor, water is escaping from the tank or supply line, the toilet keeps clogging or overflowing, or a compatible replacement part does not solve the issue. For a broader home repiping project, see our house repiping cost guide.

Sources and update note

Sources: EPA WaterSense home maintenance and EPA Fix a Leak Week. Updated October 9, 2026. Toilet designs differ; follow the manufacturer’s instructions and use a qualified plumber when the problem is beyond a simple tank adjustment or part replacement.