Are water heater elements like light bulbs in that they either work or do not work?

Question

A relative indicates that the volume of hot water delivered has declined significantly and is becoming problematic when showering. They claim the water heater thermostat set-point was upped from 120 to 140 degrees F, to increase the amount of heat delivered per volume of water and counter the issue, however, the issue persists.

Are heater elements like light bulbs in that they either work or do not work? Heater has 2 electric elements.

Any diagnostics or questions are appreciated. Especially simple tests that can confirm a bad thermostat or heating element. Thank you

Answer 1

The symptoms you describe are consistent with a failed lower element.

An electric water heater typically has two elements (and two thermostats). Only one element operates at a time.

Under normal operating conditions, the lower element will turn on when water is drawn out of the top of the tank and cold water enters the bottom of the tank. When this water at the bottom of the tank is sufficiently heated, the lower element turns off. The upper element is not activated at all.

If a large quantity of water is drawn, perhaps in excess of 50% of the tank capacity, the upper thermostat will detect cooling in the upper portion of the tank. This will cause the upper element to turn on and the lower element to turn off. When the upper element heats the upper part of the tank sufficiently, it switches back to the lower element to complete the heating cycle.

If the lower element or thermostat fails, the lower portion of the tank will never be heated. This significantly reduces the effective capacity, as only the upper portion of the tank will be heated.

If the upper element fails, you may continue to get hot water as long as the upper thermostat is not triggered. But once the upper portion of the tank cools and the thermostat triggers the upper element to come on, all heating ceases. The lower element will never come back on (because the upper thermostat is calling for heat from the upper element, which fails to provide.)

Another less-common possibility is a broken dip tube on the cold water inlet. Normally, the cold water inlet is at the top of the tank and just inside this inlet, there is a tube that extends to the bottom of the tank to direct incoming cold water to the bottom. If the dip tube has broken, cold water now enters the top of the tank, where it mixes with hot water and cools it off.

Before replacing the element, check the sacrificial anode. This is an aluminum or magnesium rod about 3/4" diameter with a steel wire core. It helps prevent corrosion of the water tank. If the rod is more than 50% consumed replace it along with the element. If it is completely consumed so that only the wire core remains, replace the entire water heater.

(If a sacrificial anode is allowed to be completely consumed, we can assume that the tank has begun to corrode and will need to be replaced soon. Better to replace the tank before it leaks than have to clean up water damage from a flood!)

Answer 2

Its possible that one of your two heat elements is not working, this can be easily tested with a multimeter. Turn off the circuit breaker feeding the hot water tank (HWT) and open the access panel to expose the leads going to the elements. Remove the power leads from the elements, and with the multimeter on the resistance or continuity setting, touch the multimeter probes to power connection terminals on the element being tested. One probe to each terminal.

The meter should indicate continuity (they usually beep) and/or show a resistance value. If it does not beep or the display shows O/L (over limit), the element needs to be replaced.

However, as you describe the problem as being one of reduced volume of hot water, it is also possible that the elements are fine but the tank has significant internal sediment buildup which has reduced the capacity. If the hot water tank is older than 10 years, and/or the water in that area contains high dissolved solids or calcium (hard water), the solution would be to replace the HWT.