The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →If your toilet keeps running, the sound alone does not tell you which part is bad. A toilet that refills on its own often has a flapper or flush-valve seal leaking water from the tank into the bowl; water that keeps flowing after the tank has refilled points more strongly to a fill-valve adjustment, blockage, or failure. Watch what the tank water does before replacing anything.
First, tell intermittent refilling from continuous running
Take the tank lid off and observe a complete flush and refill. Note whether the water stops at the end of the refill, then the toilet starts filling again later, or whether water continues to flow after the tank appears full. Those are different symptoms and call for different checks.
- It fills, stops, then starts again: water may be escaping past the flapper or another flush-valve seal. As Korky puts it in its manufacturer troubleshooting guide, “In most cases, a worn toilet flapper or flush valve seal is allowing water to slowly leak from the tank into the bowl.” That is a vendor’s general guidance, not a measured failure-rate statistic. Korky’s flapper and seal guide
- It keeps flowing after the tank fills: check the fill valve’s height and float, debris, and the refill tube before assuming the valve needs replacement. Korky’s fill-valve troubleshooting instructions
The fill valve may be turning on because the tank is losing water; hearing it run does not by itself prove that it has failed.
How to check for a leaking flapper or flush-valve seal
- Mark the tank’s water level after it finishes refilling.
- Turn off the toilet’s supply valve and wait. If the tank level falls, water is escaping from the tank, commonly past the flapper or flush-valve seal.
- Inspect the chain. Too little slack can hold a flapper partly open; chain position can also keep it from seating properly.
- Check the flapper or seal and the surface it closes against. Look for wear, damage, debris, or mineral buildup. Clean away buildup and debris where appropriate.
- If the seal is worn or damaged, replace it with one made for the toilet’s mechanism and model. If the sealing surface is cracked, warped, or damaged, replacing only the seal may not solve the leak; the flush valve or professional repair may be needed.
Some toilets use a traditional flapper; others use a tower or canister seal, or a model-specific part. Do not assume these are interchangeable. Identify the toilet and its flush mechanism before buying a replacement. Korky and American Standard both provide model-aware troubleshooting guidance. American Standard’s Champion running-toilet guidance
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How to check a fill valve that will not stop
If the tank level does not fall after you shut off the supply, but water continues flowing during or after refill, check the fill system. A misadjusted float or valve, debris, or refill-tube placement may be the cause rather than a worn-out valve.
- Check that the fill-valve height and float are set correctly and move freely.
- Where the valve instructions allow it, inspect for debris or obstruction.
- Make sure the refill tube is not pushed down into the overflow tube in a way that can cause siphoning.
- If the tank fills slowly, first check that the supply valve is open and the supply line is not kinked.
Korky’s replacement instructions call for setting the new valve below the top of the overflow tube and checking valve height and refill-tube placement if water continues to flow. Korky’s fill-valve replacement instructions
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When to replace the part—and when to adjust or clean it
| What you observe | First action | Likely part if the problem remains |
|---|---|---|
| Tank level falls with supply shut off | Inspect chain, seal, and sealing surface; clean debris or buildup | Compatible flapper or flush-valve seal; a damaged flush valve may need repair or replacement |
| Water flows on after the tank is full | Check fill-valve height, float, debris, and refill tube | Fill valve, if adjustment or cleaning does not resolve it |
| Tank refills slowly | Check that the supply valve is open and supply line is not kinked | Not established by this symptom alone; inspect the supply and valve before replacing parts |
These symptoms guide diagnosis, but they do not establish a universal failure rate or a part that fits every toilet. Fluidmaster’s instructions also identify a valve that turns on and off by itself as a sign the tank is losing water, and recommend cleaning the flapper and drain seat before changing the flush valve if leakage continues. Fluidmaster instruction PDF PART# 4-766, revision 7 (March 2017)
Replacing a fill valve
If adjustment and basic checks do not stop continuous flow, follow the instructions for the specific replacement valve and toilet. Korky’s general installation sequence is:
Rank #3
- Fits Large 3" flush valve opening
- Flapper made of chlorine resistant rubber
- Stainless steel chain attachment
- Shut off the water supply and flush the toilet.
- Remove remaining water from the tank, then disconnect the supply line.
- Remove the mounting nut and old fill valve.
- Install and set the replacement valve below the top of the overflow tube, following its instructions.
- Reconnect the supply and refill tube, turn the supply back on, and observe a full refill. If water still runs, recheck valve height and refill-tube placement.
Use the valve maker’s directions for the exact model, including any adjustment or debris-removal procedure. If flow remains low, verify the supply valve and line before concluding the new valve is defective.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When to call a plumber
Get help if the basic checks do not identify or fix the leak, if the flush-valve sealing surface is damaged, or if the toilet’s mechanism or required replacement part is unclear. A model-specific seal, a damaged flush valve, or a problem beyond the accessible tank parts may require a different repair than a standard flapper or fill valve.
Quick Recap
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- MOST UNIVERSAL the High Performance Toilet Flapper is the most universal 2 inch flapper available
- TOILET FLAPPER VALVE FITS MOST POPULAR 2 inch toilet brands including, but not limited to: American Standard, Kohler, Mansfield, & TOTO – Replaces popular rubber, float-style and rigid frame flappers
- MADE IN USA - Toilet parts flapper is proudly made in America
- QUICKLY FIX running and leaking toilets and eliminate costly water waste
- HIGH QUALITY REPLACEMENT TOILET PARTS: Need to repair or replace toilet parts? Try Korky Toilet Repair because we continue to commit to designing toilet repair parts that are universal to fit the majority of toilets. Designed & manufactured in Wisconsin.
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