The flush handle moves a lever inside the tank. If the handle suddenly moves without opening the flush valve, the lever or its connection may have slipped or broken. A handle that stays down after use can hold the flush valve open and let the tank run.
Check whether the handle returns by itself
Notice whether the handle moves freely, binds against the tank, or stays down. If you can lift the lid safely, look for the lever moving when you press the handle. Set the lid on a stable surface and avoid forcing the mechanism.
Identify the parts before replacing them
Share a photo of the lever and the toilet model if visible. Handles can mount in different positions and have different lever shapes. A plumber can check that the replacement clears the tank wall and lets the flush valve close after each use.
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