MY TOILET SOMETIMES FLUSHES ITSELF. WHAT’S WRONG WITH IT?

This is called a “phantom” flush, and it means the tank is leaking into the bowl.
 
Confirm the diagnosis by dropping some food coloring into the tank after the water has stopped running. If, after 10 minutes, the water in the bowl is colored, you’ll know the flapper is not sealing properly. If that’s the case, replace the flapper.

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