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What would be the cause of the elements to go out in my electric water heater?

My wife is convinced that it's because the water heater hasn't been drained/flushed in the past 3 years.

I was also told it was an issue with over use or possibly just old age (installed in 2004).

So for future reference so I can prevent this, what could cause them to go out?

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Thanks for the more decriptive title @Niall –  NW Tech Jul 27 '11 at 16:51
    
Almost all water heaters have two electric elements. Are you getting no hot water at all, or are you getting some, but it runs out quicker than it should? –  Michael Jul 27 '11 at 17:41
    
it was an instance of limited hot water then running out and eventually no hot water at all. both elements were replaced and seems to be back up and running. Just trying to figure out what could have prevented it. –  NW Tech Jul 27 '11 at 19:50
    
Hard to say. Sediment at the bottom can definitely cause the bottom element to quit working (hot water will run out very quickly) or break, but not the top element. Hard to guess what might have caused the top element to fail without being able to see the condition of it when it was removed. That said, if you live in a hard water area and don't have a water softener, your anode rod needs replacing unless you'e already done it or unless you've got a model with 2 anode rods (tank will have a sticker saying ~12 years, e.g. Power Miser 12,) in which case you can wait another 3 years or so. –  Michael Jul 27 '11 at 20:41
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3 Answers 3

There's a few problems. The most common is the tank rusting out. (This can usually be prolonged if you replace the sacrificial anode regularly, but it won't prevent it forever.) The second is sediment. If you have a lot of rust in your pipes or water with a lot of sediment, it can build up in the bottom of the tank. It can also build up on the elements.

Check out this website... What Kills Water Heaters

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The failure modes for an electric water heater are:

  • No hot water—or even cold water—coming through the hot water pipes. A water valve is shut off somewhere. Or there is a blocked or damaged pipe.

  • Cold water only under all circumstances: Electric supply interruption. Check circuit breakers. Check supply voltage at the tank. If the failure occurs within the water heater it is usually trivial to diagnose: check the wire connections. If those are good, check the wires to the thermostats and heaters. When they fail, it is usually quite visible.

  • Sometimes warm water, but easily depleted: power is getting to at least one of the heating elements. Check the thermostat settings—120 °F is the standard factory temperature. Check for sediment build up by opening the drain valve with power off and water supply on—it should flow freely and with a minimum of particles. Check the dip tube (in the cold inlet)—this directs incoming cold water to the bottom of the tank. Check thermostat function by adjusting the setting up and down: you should be able to hear it click or "snap" as you go above and below the current water temperature in the tank next to it.

  • Very hot water—maybe even steam. This is almost certainly caused by a thermostat failure.

The failure modes of an electric water heater element are:

  • Open: no electrical path through the heating elements. An ohmmeter measures infinite resistance between the terminals.

  • Short to ground: The outer casing of the element is an electrical conductor and grounded to the tank (or it should be). A ground short is indicated by an ohmmeter showing less than infinite resistance between a terminal and ground. The resistance between terminals can be normal, but a ground path is dangerous and will lead to early tank failure.

  • Reduced load: the heating element has decreased its power consumption. Measure the resistance across the element's terminals (disconnect wiring to one terminal to get an accurate reading):

1500 watts, 240 volt element: 38 ± 5 ohms.
2000 watts, 240 volt element: 28 ± 4 ohms.
3500 watts, 240 volt element: 16 ± 3 ohms.
4500 watts, 240 volt element: 13 ± 2 ohms.
5500 watts (commercial), 240 volt: 10.5 ± 1.5 ohms.
750 watts, 120 volt element: 19 ± 3 ohms.
1000 watts, 120 volt element: 14 ± 2.5 ohms.
1500 watts, 120 volt element: 10 ± 2 ohms.
2000 watts, 120 volt element: 7 ± 1 ohms.
2500 watts, 120 volt element: 6 ± 1 ohms.
3000 watts, 120 volt element: 5 ± 1 ohms.

A 208 volt element is rare, but use the 240 volt resistance values times 0.75. So a 2000 watt, 208 volt element should be 21 ohms.

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Sounds like a problem with hard water.

In my area the main problem is a high concentration of lime, and then it is better to use indirect electric heating.

More or less the warm water tank has a big coil in it, and the water circulating in that coil is just as warm as needed (let's say 60 degC) and your electric heater is only in contact with this circulating water. That way your heaters will live in a much nicer environment and will last much longer.

It also seems like those coils is not as sensitive to lime as the direct electric heaters since they work at a lower temperature and the lime does not "leave the water" as much when the temperature is lower.

The downside is that this installation is a little bit more expensive since you need things like a circulation pump, "expansion tank" and a "over pressure valve".

But the positive thing is that the only thing exposed to the hard water is the water tank, so this is the only thing that needs to be changed/cleaned.

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