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I rather stupidly drained my electric water heater without shutting the power off.

When I refilled it, it did not heat, which is expected. I assumed I blew the top heating element as it drained, which would have then shut off the bottom heating element or perhaps both would blow.

However, when I took out a multimeter to test, the top heating element seems OK (set to 2kΩ registers .01), whereas the bottom seems shot (registered 1.5).

I am worried I am misunderstanding something though, as I don't see how draining a water tank can cause the bottom heating element to fail, while leaving the top one intact. It seems like either both need to blow, or just the top.

Do I have my interpretation of the multimeter reading backward? Any insight would be very much appreciated.

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    My understanding is that a good element reads 15-60 ohms. Neither 0.01 ohms nor 1.5 ohms seem like good readings. – isherwood May 14 at 18:36
  • That makes sense. I guess what then confuses me is that I got a completely new 4500w element, and it read 0.01 when I took it out of the box? – evt May 14 at 19:00
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    Are you reading your meter correctly? I'm still confused by ranged meters sometimes. – isherwood May 14 at 19:03
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    @evt On kohms, you'd multiply by 1000. So 1.5 would be 1500 and .01 would be 10. depending on what the instructions say for your meter. – JACK May 14 at 19:18
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    Update for anyone curious about the resolution. Got a better multimeter, and it was only the bottom that was blown. Replaced it and it heated back up. – evt May 15 at 19:29
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The bottom element always turns on first. Cold water enters the water heater at the bottom via a "dip tube" from the top that directs the cold water to the bottom. The thermostats that control the elements are staggered. As the WH cooled, the lower element would have kicked in first, probably frying it. A lot depends upon how long it was empty. Fortunately elements aren't very expensive, you may have to replace both.

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  • Thanks, George! From the readings I reported there, can you tell which (or both) appear to be broken? Happy to replace both, but am not completely confident in my interpretation of the resistance readings (worried I am interpreting them backwards). – evt May 14 at 18:10
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You should be looking at around 13 ohms for a standard 4500 watt heating element. If an element is burned up, your meter would have 0 deflection.

Our water heaters here in Florida always have the top element going on first because that's the first water leaving the tank and getting into your shower. Once the top thermostat reaches its setting it turns off and turns on the lower element. which stays on until it gets up to its setting. The bottom element will cycle on and off during normal hot water usage but when a lot of water is being used, the top one will start to operate to keep hot water leaving the tank. I have LEDs hooked up to each element so I'm sure how they work.

My guess is that you blew the top element because it would go on first but any combination could occur depending on which one was on at the time the draining took place.

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  • Thanks, Jack! Given the readings I reported above (multimeter set to 2kΩ, reporting 0.01 on the top and 1.5 on the bottom) does that sound like I blew the top one? I am a bit confused, because I just opened up a brand new element and tested it, and it shows up as 0.01. – evt May 14 at 18:39
  • @evt Check your ohm scale and your scale multipliers. Hopefully, you have an analog meter... – JACK May 14 at 18:48
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    @GeorgeAnderson Meant 0 deflection. Are you sure about the elements? You're right about water entering from the bottom of the tank through the dip tube. When the tank is fill, which is when you'd turn on the breaker, the top element would come on first to heat up the water so you'd have some hot water fast because that water would exit first. Once that got up to heat, then the bottom kicks in to finish off the lower, colder water entering the tank. – JACK May 14 at 21:34
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    @JACK completely agree! I was referring to more normal operation and moderate hot water usage. On a newly filled, cold tank, the top element would surely come on first, then when it reached setpoint the bottom element would come on. In my previous house, after an extended power outage, when power was restored, we didn't get any hot water. Turned out the top element was burned out, for who knows how long?! So the top Tstat wouldn't turn on the bottom element until the top was at set point, which wasn't going to happen with a burned out element! – George Anderson May 14 at 23:05
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    @GeorgeAnderson Completely agree with your normal operation and moderate usage scenario. – JACK May 14 at 23:15

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