Troubleshooting Electric Water Heater

[frank1492]

Hello- I was away from my winter home for about 3 months over the summer. Before leaving, I shut off the power supply to the heater and shut off the water supply to the house. This year I did the same as always: When I returned I turned on the water supply and checked to see if there was a steady stream from both faucets at the sink closest to the tank as per manu instructions so not to blow the elements. (Sink is about 6ft away.) The hot water came up nicely, as usual. Today (one day later) the water was cold. I pressed the high temp overload button but was not sure it had popped out- the excursion is so slight. A few minutes later the water started to heat. There was voltage across the upper heating element, but none at the bottom. Would anyone know if that is normal and does the lower element only kick in when necessary? (If so, please define "when necessary.") After1/2 to one hour now the water is at full temp and the lower element still has no volts, but I still wonder when the water is ice cold the two don't come on at the same time. (Assuming this has nothing to do therefore with why the water was cold to start with.) Is the problem with the limit button or something else? (*NOTE* I did see to make sure the retaining springs were pressing the thermostats hard against the tank and while they did "rock" a little, they seemed fine.) And should I wait to see if it happens again? Thanks so much for your help! Frank

[Colbyt]

Frank,

The average residential heater never has more than one set of elements on at any given time due to the load involved. I only own two of them and I don't recall the proper sequence for heating. I seem to recall it is series wiring but don't hold me to that. Generally by the time I know I have a problem both elements are dead and need replacing so I just but two and go. :)

I would wait and see on this one. If you continue to have hot water I would do nothing.

[Ron in NY]

From a cold start, the upper element will come on to heat the upper part of the tank because that is where the hot water exits. After the top thermostat has been satisfied, the upper thermostat switches power to the lower thermostat which in turn sends power to the lower element. After the water at the bottom of the tank is hot enough, the lower thermostat cuts power to the lower element.

When you start to draw hot water, it is drawn from the top of the tank, and cold water enters through the fill pipe which is extended inside the tank somewhere near the bottom. The lower thermostat senses the bottom of the tank is getting cold, and activates the lower element and starts to heat the bottom of the tank. If you draw enough hot water and the top of the tank starts to drop in temperature, the upper thermostat will cut out the power feed to the lower thermostat and activate the upper element to try and keep the water at the top of the tank hot so you don't run out of hot water. Hope that clears it up.

RON ======================================================== Remove the ZZZ from my E-mail address to send me E-mail.

[frank1492]

Thanks Ron, great explanation. I should have realized the two elements couldn't be on at the same time. I will look occasionally to see if the bottom element has juice as I have never found any. It occurs to me that if the switching mechanism failed, the bottom part of the tank would never get heated separately and one might not be the wiser except the hot water would get cold sooner. How exactly is the switching accomplished? Thanks again. Frank

[Ron in NY]

One leg of the 240 volt electric supply is always connected to both elements. The upper thermostat incorporates a SPDT switch within it. In one position it supplies the other leg to the upper element, and when the water gets hot enough at the top of the tank to reach the upper thermostat set point, the upper thermostat switches that leg to the lower thermostat which in turn supplies it to the lower element until the bottom of the tank reaches the lower thermostat set point. When both thermostats are satisfied, neither element is supplied. As you draw hot water, the lower element will come on first as the hot water is replaced by the cold water coming into the heater. If you keep on drawing enough hot water, and deplete its supply, eventually the upper thermostat will cool off and will switch the power to the upper element. The upper element usually is not used unless you deplete the supply of hot water to the point where the top of the tank cools off. I hope this explains everything.

If you never see any power at the lower element, either the lower thermostat has gone bad, or the SPDT switch in the upper thermostat has gone bad.

RON ======================================================== Remove the ZZZ from my E-mail address to send me E-mail.

[Red Green]

[e-mail] (Ron in NY) wrote in news: [e-mail]:

Ditto and on the money.

Good explanation. Better than I ever did trying to say the same thing.