I have a 4 yr old AO Smith water heater. Last year the water began getting too hot frequently triggering the reset button. I tested the thermostats and elements. It looked like the issue was the top thermostat so I changed. Recently the problem is back and more frequently. I have tested the thermostats and elements with a continuity tester and multimeter ... all test positive and working.

It has been recommended I change the bottom thermostat first and then if that does not work, change elements too.

Any ideas on what might be going on?

It's tripping because of over-temp. Your problem cannot be the elements. It has to be a thermostat.

Elements CAN fail and still heat, and cause overheating. I am not sure if your testing was done properly, so cannot verify tht the elements are actually working properly. I have replaced thousands of elements but only a handful of thermostats.

I'm missing something in the logic. If, as I leave a room I turn a light switch off, and the light doesn't go off.......should I replace the bulb?

correct.. you just need a couple of guys to turn the ladder..

or, if you are a cardio/thoracic surgeon, the building will rotate around you

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

His problem is very likely a thermostat issue but it could be an element. An element can blow out but maintain a ground from the outer sheath to the tank. An amp test will show minute amperage draw but it is constant and will eventually trip the ECO.

They come in a kit together....replace both thermostats and elements and be done with it.

Thanks m&m.......That would do it. I think that can be checked with a volt meter also.



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You have to have MORE EXPERIENCE with electric heaters. The thermostat only controls ONE LEG of the power to the element. IF the element burns out in the "right place", the water will act as the ground and the "live leg" of the power will continue to heat the water with 120 v. and will CONTINUE to do so until the water overheats and trips the high limit.

A voltmeter will tell if they SHOULD be working, an ammeter tells you if they ARE working.

A volt meter can't be used to look for that particular problem?

NO! All it tells you is that there is voltage going TO the element. It cannot tell you if it is actually doing anything.

1. Test the voltage at the element. If it is 120 v. the element is shorted out. If it is 240 go to next step. If it is zero, the there is either no power to the heater, the high limit may have tripped, or the upper element may not be working.
2. Test the amperage at both wires to the element. IF both are zero, the element is burned out. If one has amperage and the other does not the element is shorted out. IF both are the same, the element is good.



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Would a voltage drop test across the element point to that problem?

It will only be zero, 140, or 240. But by itself voltage may not diagnose a problem, it can indicate you have one, however.