low voltage on water heater elements


Old 01-25-05, 11:49 AM
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low voltage on water heater elements

What would be the effect of 208 volts on an element in an electric water heater that is designed for 240 volts? I have replaced both top and bottom element as well as both top and bottom thermostats. I get hot water for a while and then nothing. The tank is cold all over.
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Old 01-25-05, 12:33 PM
Join Date: Sep 2000
Location: United States
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I would imagine that applying 208 volts to a 240-volt water heater would work just fine, but it will take significantly longer to heat up the water.

The symptoms of hot water for 5 minutes and then cold is typical of a failed dip tube. Next time this happens, tap off a little water from the drain valve at the bottom of the tank. If that water is still hot, then this confirms the dip tube problem. Water heaters manufactured between 1993 and 1996 (check the label on your tank) had defective dip tubes.
Old 01-25-05, 01:25 PM
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John, Thanks for the quick comeback. Let me further explain in detail what my problem is. The water heater involved is at our church. Another church member approached me with these details. The heater is a year or so old. He replaced the top element a few weeks ago and admitted to me that he turned the power on before the tank was full. He said he had hot water for a while(day or two?) then, cold again. He then replaced both elements and both T-stats and still no hot water. He gets 208 volts at the top T-stat(the tank is a long distance from the breaker box). Today, I was at the church and while there, felt of the hot outlet pipe and it was as cold as the inlet. The 240V breaker was on. I plan to ring out all the wiring on the heater this week to locate the open cicuit that I suspect is causing the problem. I wasn't sure if 208 volts would damage the elements in a short time. Thanks in advance for any hints.
Old 01-25-05, 02:17 PM
Join Date: Jan 2002
Location: Chicago
Posts: 1,915
208V will not damage the element, it will simply not heat up as much. The element is just like a light bulb...lower voltage means it won't be as bright. Turning on the power before the elemet is submerged will burn an element very, very quickly. Check for voltage at the elements. Generally only 1 element turns on at any one time, first the top, then the buttom when the top water is hot. If you have voltage then the element is bad. If not, the T-stat is probably bad.
Old 01-26-05, 10:46 AM
Join Date: Sep 2001
Location: Yorktown, VA
Posts: 322
trinitro's description of how the top heats first and then the bottom is by far the most common way a water heater is wired. If that's the case, a non-functioning bottom element will give symptoms much like you described...hot water, but for a short duration. I said non-functioning because it could be a bad element, bad lower thermostat, bad upper thermostat, or bad wiring.

If the top element is not functioning, then it is unlikely that you will have any hot water at all, since the bottom element doesn't work until the top thermostat is satisfied.

Is it possible that when the elements and thermostats were replaced that something didn't get wired back correctly?

By the way, some elements actually have the wattage for both 208 and 240 volts stamped in the base.

Good luck,
Old 01-26-05, 01:56 PM
Join Date: Feb 2003
Posts: 525
When measuring the voltage at the "top thermostat", was the measurement taking above the reset button (which is attached to the top of the upper thermostat)? If so, is it possible that the reset button has tripped which cuts the power to the entire unit? If it has tripped, there is a reason. Either the reset button is defective (they aren't supposed to trip unless the water temperature way exceeds the normal settings (but before the boiling point), which is unusual in my experience, or it's more likely that the "technician" wired something wrong (like direct wired the upper element) which caused the element to operate until the water got so hot that it tripped the reset. The water in the tank would provide hot water for a good while before it tempered down.

Not all upper thermostat / reset button are wired alike which may have led to some confusion.

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