The inlet valve does not regulate refill correctly. The same symptom can have several causes, so avoid replacing parts before identifying the source.
What to do first
Stop flushing if the bowl is backing up. If water is escaping, close the supply valve when safe. Avoid harsh chemicals and excessive force on porcelain components.
When to get professional help
Recurring problems, active leaks, visible cracks, or backups involving other fixtures deserve further assessment.
Related service: Toilet Fill Valve Repair.
