Start with the symptom and the access panel
When water continues running into the bowl, the problem may be a worn outlet seal, a poorly seated flush valve or a filling valve that never closes fully. A button that feels loose can have a different cause from a cistern that refills repeatedly. We first establish the make and approximate age of the toilet, whether the flush plate is removable, and what can be inspected through the manufacturer access opening. Opening finished tilework is not the first step just because the reservoir sits behind a wall.

