Two possibilities. 1 failed upper or lower Tstat 2 Shorted element To test element: disconnect both wires to element terminals. use continuity tester to see if there is continuity through element (one probe on each element terminal) If no continuity element is bad. Then test for continuity between each element terminal and the water heater itself.( one probe on element terminal and one probe grounded on bare metal or inner tank.) If there is continuity from terminal to ground, element is bad and also can cause tank to continue heating even when thermostat shuts off. This is because the thermostat only shuts off one pole of the 220 and a shorted element can continue heating from the 2nd pole. If both elements test OK and water heater heats the full tank( tank feels hot at bottom element access panel when no hot water for 2 hours) most likely the lower thermostat is bad.
Answers & Comments
Two possibilities. 1 failed upper or lower Tstat 2 Shorted element
To test element: disconnect both wires to element terminals. use continuity tester to see if there is continuity through element (one probe on each element terminal) If no continuity element is bad. Then test for continuity between each element terminal and the water heater itself.( one probe on element terminal and one probe grounded on bare metal or inner tank.) If there is continuity from terminal to ground, element is bad and also can cause tank to continue heating even when thermostat shuts off. This is because the thermostat only shuts off one pole of the 220 and a shorted element can continue heating from the 2nd pole.
If both elements test OK and water heater heats the full tank( tank feels hot at bottom element access panel when no hot water for 2 hours) most likely the lower thermostat is bad.