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How to Repair a Running Toilet Flapper
Identify the cause of your running toilet using a simple dye test. Follow these steps to replace the flapper and restore proper function.
Perform a Diagnostic Dye Test
Add food coloring to the tank and wait 15 to 30 minutes without flushing 1. If color appears in the bowl, the flapper or flush valve seat is leaking 1. If the tank level drops but the bowl remains clear, the issue is likely the fill valve, float, or refill tube 1.
Drain and Clean the Tank
Turn off the water supply valve and flush the toilet to drain the tank 13. Wipe the flush valve seat with a scouring pad or cloth to remove mineral deposits that prevent a proper seal 13.
Remove and Size the Flapper
Disconnect the chain and remove the old flapper 17. Measure the flush valve opening, which is typically 2 or 3 inches, or bring the old part to the store for an exact match 17. Avoid relying on universal claims without verification 17.
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Install the New Flapper
Attach the new flapper to the flush valve 11. Connect the chain to the flush lever, ensuring 1 to 2 links of slack to prevent the flapper from being held open 11.
Check the Refill Tube
Ensure the refill tube is clipped to the side of the overflow pipe 11. The tube must not be submerged, as this causes siphoning and mimics a leaking flapper 11.
Remove Chemical Cleaners
Remove any in-tank bleach or chlorine tablets 15. These chemicals degrade rubber components and cause premature failure of the new flapper 15.
Sources
Every step cites the sources below. Facts are rechecked automatically every 60 days or whenever a reader flags an error.
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