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Fix a Running Toilet
Explore the parts inside a toilet tank, see how a flush works, and follow simple checks to help find why your toilet keeps running.
- Task
- Basic plumbing check
- You need
- Towel, flashlight, manual
- Rule
- Manufacturer instructions control
This guide shows a common gravity-flush toilet with a rubber flapper. Pressure-assisted, canister, and dual-flush toilets may work differently. Follow your toilet manufacturer’s instructions.
Supplies
- Towel
- Flashlight
- Manufacturer’s instructions
- A compatible replacement part only if needed
This page also offers an interactive 3D walkthrough with rotation, zoom, and step-by-step animation when JavaScript is enabled.
Complete written walkthrough
- 1
Step 1 — Look before adjusting.
Carefully remove the lid. With the water on, look without touching: is water flowing into the overflow tube, or does the toilet refill from time to time? Water entering the overflow points toward the water-level setting or fill valve. Occasional refilling may indicate a leaking seal.
Observation first helps you guess which part is involved before you touch anything.
- 2
Step 2 — Turn off the water.
Close the toilet’s supply valve gently. Do not force it. Flush to drain most of the tank and confirm that it does not refill before handling parts.
If the valve will not shut off, stop and contact a plumber rather than forcing it.
- 3
Step 3 — Check the handle and chain.
Make sure the handle returns freely and the chain is not caught. Follow the manufacturer’s chain adjustment instructions so the flapper closes fully and lifts properly.
A chain that is too tight can hold the flapper open; one that is too loose can catch under it.
- 4
Step 4 — Check the flapper.
Look for damage or debris that could prevent a seal. Gently clean the sealing surface as the manufacturer allows. Replace a worn flapper with the correct part for your toilet.
Similar-looking flappers are not always interchangeable. Match the part to your toilet model.
- 5
Step 5 — Check the fill system if needed.
If water was flowing into the overflow tube, follow the manufacturer’s instructions for the float and fill valve. Use the specified tank water line. Do not bend parts or use a universal adjustment measurement.
Adjust only as the manufacturer describes for your fill valve and float type.
- 6
Step 6 — Restore water and test.
Slowly reopen the supply valve. Watch a full flush and refill. Confirm that filling stops, the flapper closes, and no water leaks outside the toilet. If running continues, turn off the supply and seek help.
A complete flush and refill is the real test that the repair worked.
Frequently asked questions
Why does my toilet keep running?
A flapper that does not seal, a caught chain, or a fill valve that does not stop can let water keep moving. Check what the water is doing before buying a part.
How can I check for a silent leak?
With the tank full, add a few drops of food coloring to the tank. Wait 10 minutes without flushing. Color appearing in the bowl indicates a leak. Flush immediately afterward to help prevent staining. This test finds a leak; it does not identify the exact faulty part.
Will any replacement flapper fit?
No. Match replacement parts to your toilet model and flush system. Check the model number, owner’s manual, and manufacturer’s parts list.
What if my toilet has no rubber flapper?
It may use a different flush mechanism. Use the manufacturer’s instructions rather than following the flapper replacement steps.
When should I call a plumber?
Get help if the shutoff valve will not close, parts are damaged or unfamiliar, water leaks outside the toilet, or the problem continues after basic checks.
Before you finish
Parts should match your toilet model
Similar-looking parts are not always interchangeable. Match replacement parts to your toilet model and flush system using the model number, owner’s manual, and manufacturer’s parts list.
When should I call a plumber?Get help if the shutoff valve will not close, parts are damaged or unfamiliar, water leaks outside the toilet, or the problem continues after basic checks.
Sources and scope
This guide shows a common gravity-flush toilet with a rubber flapper. Pressure-assisted, canister, and dual-flush toilets may work differently. Follow your toilet manufacturer’s instructions. Repair guidance was checked against publicly accessible toilet and component manufacturer instructions; no professional review is claimed.
General guidance reviewed September 19, 2026.