My 240v electric water heater is approximately 5 years old and stopped heating yesterday. I followed some online advice and found the breaker inside the top access panel tripped. I reset the breaker and checked for voltage at both elements. I cut the power at the house breaker and removed the wires from both heating elements and tested for continuity and shorts to ground on both heaters. Both elements has about 15 ohms resistance and were open to ground (heater tank ground wire inside lower access panel). I restored power to the heater and checked current draw on both elements with a clamp on ammeter. I found 17.5A to the upper element and 1.5A to the lower one. The water was plenty hot last night and this morning but this afternoon the water is cool and I found the breaker tripped again. Have I missed a step in my diagnosis? Could I have a short inside one of the thermostats? Could a bathtub faucet drip cause the heater to run too much and overheat the breaker inside the heater? An expert opinion short of replacing the unit would be very helpful.

Disconnect one of the elements. See if it happens again, I would suspect the other element.

To diagnose things like this, you would need a min/max meter and a clamp on ammeter.