Controls do go bad and they are not difficult to replace.
Should be 2 of them : upper and lower.
Another possibility is that one of the elements has
developed an internal short or "leakage". That can
cause overheating that the thermostat can't prevent.
Another thing that can cause an electric water heater to overheat is a
situation where one of the thermostats is for some reason pulled back from
contact with the side of the tank. Most thermostats are held against the
tank by simple spring action. The back of the thermostat should be in
direct contact with the tank.
The element either works, or is open and does not work at all. The element
is controlled by an thermostatic on-off switch which could be defective or
not making good physical contact with the tank and thus is not sensing the
temperature as it should.
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