Hot water heater is dispensing ultra-hot water.

Old 03-29-11, 07:54 AM
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Hot water heater is dispensing ultra-hot water.

Hey everyone,

I have a 50gal electric water heater in my house that has two thermostats; an upper and lower. Recently, the water in the house has been getting dangerously hot. I went to the panels on the water heater and switched both panel thermostats from A (Scale: Dot [Off?], Hot, A, B, C, Very Hot) to Hot. The water in the house didn't cool down at all. I then set the top thermostat to the Dot settings, which I assume was Off. Using a Multi-meter, I checked the heating element to see if it had current with the thermostat set to that setting and it did. I figured the thermostat was bad and that it was constantly heating without sensing the temperature of the tank via some contact sensor. I went to Home Depot and bought a new thermostat and installed it. I set the temperature to 100 or so and let it sit for a few hours. Before bed I let the kitchen faucet continuously fill a glass of water in which I had a meat thermometer. The temperature read 175F.

One concern is I have a mix of PEX and Copper throughout the house. I know those temperatures are pushing the limits of PEX. I'm unable to tell if there has been any damage to the pipe already but as a precaution, I have it powered off by killing the breaker in the circuit breaker box.

When I went into the closet yesterday I noticed a small puddle of water around the tank. I traced it to the discharge pipe. I assume this is because the water is too hot?

What is the root of this problem? Is there something else I need to check or try replacing? Could the issue be a faulty circuit breaker or something else?

I'm looking for any suggestions so I can fix this ASAP.

Many thanks in advance.
Old 03-29-11, 08:27 AM
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First..a quick explanation. The upper element initially starts heating (assuming a cold tank), when it is satisfied, it switches to the bottom element. did you measure current? Did you mean voltage? If so..what was the reading? Not sure of the exact way of measuring, but IIRC you will always have 120 on one side of the element/thermostat (not sure which or if its both). When the element is energized you'd see 240.

Yes the water is from the temp and press relief valve, it's doing what it's supposed to. And yes, that high a temp could cause issues. I'd cut the power, drain some and refill. That should give you some hot water til its fixed.

Let some Pro's check in and plz answer the above questions.
Old 03-29-11, 08:29 AM
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Probably the lower t stat. Its in runaway mode, and usually the upper t stat breaker will trip if the heater gets too hot.

The lower t stat is the more common one to fail.

Mike NJ
Old 03-29-11, 11:04 AM
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(Moderators, you may want to make this a sticky.)

The wiring from the source to the elements is as follows: The two source wires go to the manual reset high temperature cut out. From there one side of the source goes to both elements. This means that if you measure voltage at the elements by connecting one meter lead to either element connection and the other meter lead to the steel shell of either the tank or the sheet-metal wrapper you will measure 120 volts. (assuming the high temperature cut out hasn't tripped.)

The other source wire comes from the high temperature cut out and goes to the "common" terminal of the upper element thermostat. The "normally closed" contact of the upper thermostat is connected to the other terminal of the upper element with the "normally open" terminal of the upper thermostat connected to the lower element thermostat and finally a wire from the lower element thermostat to the other terminal of the lower element.

The action of the upper and lower thermostats is as follows: With a cold tank the upper thermostat will route power to the upper element through the normally closed contact. This heats the water in the upper 25-33 percent of the tank giving usable hot water in a reasonable time frame. Once this upper part of the tank reaches the "set point" of the upper thermostat it will open the connection to the upper element and close the connection to the lower thermostat. The lower thermostat will route the power to the lower element heating the water in the rest of the tank until the lower thermostat opens and then both elements are effectively off.

This wiring and thermostat action is why you MUST measure the voltage across the two element terminals and NOT from one terminal to the steel. This voltage should measure 240 volts (+/- 10%) when the thermostat for the particular element is on and 0 volts when the assigned thermostat is off. Measuring from either element terminal to the steel ("ground") will ALWAYS give a reading of 120 volts regardless of the thermostat position as long as the element is internally intact.

One fault that is often overlooked is when an element becomes "grounded". This happens when there is a fault internal to the element that causes the internal element to be connected to the sheath of the element. If this happens the element will be constantly heating at a lower rate because of a complete circuit being made from the one unswitched source wire, through the element and internal fault to the steel of the tank. This continuous operation, even though at a reduced voltage can and does cause overheating of the water during periods of low water consumption like overnight.

To check for a grounded element it is necessary to remove all power from the heater by "opening" (turning off) the circuit breaker or local disconnect serving the water heater and check each element independently by removing the wiring from the element (both wires) and setting a multimeter to the "Ohms" position or "Continuity test" position. Connect one meter lead to the element terminal and the other meter lead to the steel tank. There should be infinite ohms resistance or no continuity. Check the other terminal of the element the same way and then check the other element in the same way. If you find a grounded element it must be changed.

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