Check the water level in the tank; it should be about 1 inch below the overflow tube rim
If the water level is high, adjust the fill valve float or float cup downward to lower the water level
Inspect the flapper for gaps, warping, cracks, or debris preventing a tight seal
Clean the flapper and the flapper seat; remove mineral buildup or sediment
Re-seat the flapper on its hinge and ensure the chain has proper slack
Adjust the flapper chain so there is slight slack (not tight, not too long)
If the flapper is worn, replace it with the correct type for your toilet model
Inspect the fill valve; ensure it is not sticking or water leaking into the overflow tube
If water runs into the overflow tube, replace the fill valve assembly
Check the overflow tube height; ensure it matches the manufacturer spec and is not set too low
Verify the flapper is not hitting the overflow tube or getting caught on tank parts
Test for leaks by adding a few drops of food coloring to the tank water and watching the bowl for 10–15 minutes; replace parts as needed if color appears
Tighten loose tank bolts and connections if water is leaking around the tank-to-bowl seal
Replace the tank-to-bowl flapper seal/gasket if the toilet runs due to a faulty seal
Confirm the handle and lift wire are not holding the flapper open; adjust or replace the handle/lift mechanism if needed