Watch what happens after one flush
- Set the tank lid on a padded, stable surface.
- Flush once and watch the linkage, flapper or canister, fill valve, float, refill tube, and waterline.
- When the tank looks full, check the overflow tube. Water should not keep flowing into it. [1]
- Wait a few minutes. If the fill valve starts again without another flush, water is probably escaping through the flush seal or another tank-to-bowl path.
- If the water keeps rising, use the fixture shutoff only if it turns normally. Record the toilet and fill-valve model before changing any settings or parts.
Match the sound to where the water goes
| What happens | Most relevant checks |
|---|---|
| Water spills into the overflow tube | Float setting or movement, debris or wear in the fill valve, and model-specific fill-valve height. |
| Tank goes quiet, then refills later | Flapper or canister seal, flush-valve seat, chain slack, and part compatibility. |
| Chain stays tight at rest | Handle alignment and enough slack for the seal to sit fully on its seat. |
| Seal closes but dye reaches the bowl | A dirty, distorted, worn, or incorrect seal, or a damaged flush-valve seat. |
| Refill tube keeps sending a strong stream | The fill valve is still open; the float or valve has not reached shutoff. |
Check a silent tank-to-bowl leak with dye
Wait for the tank to finish filling
Start only after the fill valve stops.
Add dye to the tank
Use a few drops of food coloring or a dye tablet. Do not put it in the bowl.
Wait without flushing
After about ten minutes, color in the bowl confirms that tank water is leaking past the flush seal. [1]
Flush afterward
Clear the dye promptly to reduce staining. [3]
Identify the exact part
Use the toilet model, valve size, and seal design. EPA recommends checking the owner's manual or manufacturer information before choosing a replacement. [3]
Why an adjustment may not fix it
Lowering the float can help when the waterline is simply set too high. It will not repair a fill valve that cannot close, a leaking flush seal, or a cracked overflow tube. Randomly shortening the chain or weighting the flapper can also weaken the flush or keep the seal from closing.
Toilet seals wear, including on models that originally met WaterSense requirements. [2] Use a part made for the toilet, restore the specified waterline, test several flushes, and repeat the leak check.
When the first repair does not solve it
- A new flapper still leaks because it does not fit or the flush-valve seat is damaged.
- The fill valve stops correctly, but a separate flush-seal leak lowers the tank level and starts it again.
- The handle binds and keeps tension on the chain or linkage.
- A cracked overflow tube, tank, supply connection, or shutoff adds an external leak to the running-water problem.
- The parts are brittle, heavily scaled, or too model-specific to adjust safely by trial and error.