Toilet
What causes my toilet to keep running after flushing?
Use the tank water line, overflow tube, flapper seal, chain slack, handle return, and fill valve behavior to narrow a running-toilet symptom safely.
Direct answer
A toilet usually keeps running because water escapes from the tank into the bowl or the fill valve never reaches a clean shutoff. Identify the tank part and symptom before buying a repair kit.
Tank-part identification diagram
Handle lever -- chain -- flapper over flush valve
|
Water line mark ---------|-- overflow tube opening
|
Float cup/ball -- fill valve -- refill tube clipped to overflow tube
Supply line -- shutoff valve below tankSymptom table
| What you see or hear | Likely part area | Safe check | Stop point |
|---|---|---|---|
| Water runs into overflow tube | Float height or fill valve shutoff | Compare water level with tank mark and observe whether float rises freely. | Do not force the shutoff valve or replace a fill valve if the supply valve leaks. |
| Water trickles into bowl with tank quiet | Flapper, flush-valve seat, chain tension | Check for chain trapped under flapper and inspect flapper surface. | Stop if flush-valve seat is cracked or tank bolts/gasket leak. |
| Handle sticks down | Handle lever, nut, or chain slack | Lift handle and see whether lever returns freely. | Do not overtighten the handle nut; many are reverse-thread or plastic. |
| Intermittent refill | Slow flapper leak or flush-valve seal | Use a dye test only after the bowl is clean and no cleaners are coloring water. | Stop if toilet rocks, leaks at base, or floor is soft. |
| Hissing after refill | Fill valve not shutting off cleanly | Identify fill-valve model and tank brand before buying replacement. | Call a plumber if the angle stop is stuck, corroded, or dripping. |
Model-specific part compatibility
Bring a photo of the inside tank, brand stamp, tank model number, flush-valve size, flapper style, and old part number if present. Universal parts are not universal for every canister valve, dual-flush tower, pressure-assist toilet, or specialty tank.
Dye-test caveats
- Use a few drops of food coloring only in the tank and wait without flushing.
- Blue tank additives or recent cleaners can make the test hard to read.
- A positive dye test identifies tank-to-bowl leakage; it does not prove which part fits.
Sources used
- EPA WaterSense residential toilets.
- EPA WaterSense Fix a Leak Week.
- Fluidmaster, Korky/Lavelle, Kohler, American Standard, and TOTO tank-part instructions for model-specific fill-valve, flapper, canister, and dual-flush compatibility.
Safety note: Shut off water before repairs when appropriate. Call a qualified plumber for sewer backups, major leaks, gas appliances, approvals, or work you are not confident completing safely.