Some symptoms of a worn toilet tank valve are humming and constantly running water. The tank valve is responsible for filling the toilet reservoir with water in preparation for flushing. As tank valves become worn out or damaged, they limit the ability of water to flow smoothly through the valve.
This causes a slight humming or, in extreme situations, a screaming to issue from the tank as it fills with water.
Another symptom is the constant sound of running water. This symptom could be due to either the tank valve or the flapper, which controls the flow of water into the toilet bowl. Troubleshoot the problem by mixing dye into the water in the toilet tank. Wait and see if the dye appears in the toilet bowl. If it does then the problem is the toilet tank flapper. Otherwise, the running water is due to the tank valve.