Check the water level in the tank; adjust the float/ball or fill valve so the water sits at the marked level (usually about 1/2 inch below the overflow tube)
Inspect the flapper for wear, warping, or debris; replace the flapper if it doesn’t seal properly
Clean the flapper seat and overflow tube area; remove mineral buildup or debris
Adjust the flapper chain length so there’s slight slack (not tight, not dragging)
Ensure the flapper lifts fully when the handle is pressed; check for binding or misalignment
Verify the fill valve is functioning correctly; replace the fill valve if it won’t shut off fully
Check the overflow tube; confirm the water level is below the top of the overflow tube
If the toilet has a flapper with a float rod, adjust the float rod height to stop the refill at the correct level
Inspect the toilet handle and lift arm; tighten loose connections or replace worn parts
Check for leaks from the tank to the bowl; add a few drops of food coloring to the tank and wait 10–15 minutes—replace/adjust the flapper if coloring appears in the bowl
If the leak appears to come from the tank bolts or tank-to-bowl gasket, tighten bolts gently and replace the gasket if needed
Inspect the shutoff valve supply line; turn off the water, remove the line, check for debris, and reinstall
Clean or replace the fill valve inlet filter (if present) if the tank refills oddly or won’t shut off
After repairs, flush several times and confirm the running stops and the tank refills to the correct level