Water heater elements

[homnspector]

A plumber once told me how to test a water heater element with a continuity meter. I forgot the process, I know you had to disconnect some conductors from the terminals. Anybody know the process?

[fqp25]

If you have a multi-tester or a tester with an "Omega" symbol you can test the resistance. Hook up both leads to the terminals of the element. If the element is OK you should read some kind of number. If the element is burned up then the reading should be nothing, because the element is "open"

Just like if you touch the 2 leads together, you'll get a reading, and if you leave them apart you'll get nothing.

Hope this helps; I know it's not to descriptive.

[Robert E Lee]

I don't believe I would use that method, a better way is to use a clamp on amp meter placed around one of the wires leading to the heating element, then turn up the water temperature thermostat. If the element is good you will see a current reading on the meter, on dual element water heaters only one of the elements will operate at a time. Most often a failure will be found at the bottom element as this one is used whenever a quantity of hot water is drawn.

Robert E Lee

GENERAL Home Inspections, Inc

[Jerry Simon]

"on dual element water heaters only one of the elements will operate at a time."

If you run the heater out of hot water, both elements will operate at the same time.

[Rich Rushing]

Jerry,

Not so... Here's how it should work:

When a water heater is at rest, the tank will be filled with hot water (no need for the element to be on). When a hot water faucet is turned on in the home, hot water is taken from the top of the tank and cold water is again supplied at the bottom through the dip tube. The cold at the bottom of the tank activates the thermostat for the lower element. The lower element then comes on and heats the incoming cold water. The upper element will still be surrounded by hot water and will be satisfied.

When hot water continues to be drawn, the tank will then be filled with cool water because the lower heating element will not be able to warm the water quickly enough as it comes in. After a while, the hot water will be drawn off up to the level of the upper thermostat. Now, both thermostats are calling for heat. Since only one element can operate at a time, the upper element has priority and will shut off the lower element.

The upper element has priority because after the tank has run out of hot water, the upper element is the fastest way to replenish the hot water. Since the water is drawn off the top first, the upper element heats the water near the top of the tank. Once it heats the water in the top part of the tank, the thermostat will be satisfied and the upper element will shut off. The lower element now gets electricity and heats up the water in the lower two thirds of the tank.

Under normal conditions, the lower element is in operation the majority of the time, although the upper element has priority.

Rich Rushing

[Joshua]

Originally posted by Jerry Simon

"on dual element water heaters only one of the elements will operate at a time."

If you run the heater out of hot water, both elements will operate at the same time.

I don't see how they can do that. The upper thermostat is a single-pole double-throw switch. When it senses adequate heat, it connects one side of the 220 to the lower element. The lower thermostat is a single-pole single-throw switch. When it calls for heat, it closes the circuit. However, when the uppper element also calls for heat, its thermostat sends current through the upper element, cutting off the lower one.

Since only one side is switched, there is voltage present at all times in both elements, but there isn't current on more than one element at a time.

Cold water is introduced to the bottom of the tank. If the water in the top is still hot, only the bottom element operates. When the water in the top is also cold, the top element takes over and the bottom one stops.

[hausdok]

Hi Fritz,

Back to your question - yes, there are test protocols you can use to check the voltage to the unit, the high-limit temperature cutoff, the thermostats and the heating elements. I have several sources, but the simplest description, including illustrations, that I have comes from the Time/Life Fix-it-Yourself series issue on kitchen and bathroom plumbing. There's a whole section about diagnosing and repairing conventional tank-type gas and electric water heaters - including trouble-shooting charts.

Here's an electric water heating testing protocol adapted using that text. Some of this is word-for-word from the Time/Life text but I've paraphrased the text where necessary. I am not advising you to do this. I'm just answering your question the best way I know how.

You'll probably never see me monkeying around with a water heater like this, but if you're comfortable around electricity and have a mind to you'll have to be your own best judge. Cut it and paste it if you want to, but don't use this protocal until you've practiced it on an actual water heater a few dozen times to memorize it and get it down pat, or you're going to look pretty silly - not to mention incompetent - sitting there reading those instructions and trying to follow them on an actual inspection.

ONE TEAM - ONE FIGHT!!!

Mike

Checking the Water Heater Controls

1. Checking the voltage at the disconnect switch box. Shut off the house's main power switch at the service panel, and label it so that no one will turn it on. Then access the water heater controls by removing the covers and insulation.

If the water heater has a disconnect switch box, turn it off.

Use a multi tester (multi-meter) set at 250 volts AC to verify incoming power to the switch box.

Caution: Do not touch the switch box. Hold the tester probes by the insulated handles only and touch one probe to each of the upper terminals.

The tester should read between 200 and 250 volts.

Next touch one probe to the left terminal and the other to the grounding screw on the back of the box.

The tester should read about 120 volts. Test the right terminal the same way. If all results are between 200 and 250 volts go to step 2. If not, refer it to an electrician for repair.

2. Testing the lower terminals. With the power on, test the two lower terminals as you tested the upper terminals in step 1; the results should be the same.

If all the readings on both steps are what they should be, enough power is getting to the heater. If not, call an electrician.

Before working on any part of the heater, test that the power is off: Shift the lever arm of the disconnect switch box to the OFF position and test the lower terminals as you tested the upper terminals in step 1. This time the tester should show 0 volts in all cases.

If the tester shows that the disconnect switch box conducts any power at all while in the OFF position, do not touch the switch box or the water heater; refer it to an electrician for repair.

3. Verifying power shutoff at the heater. Set the multi tester at 250 volts AC and touch a probe to each of the upper terminals of the high-limit cutoff (the one with the red reset button) above the upper thermostat. Then touch one probe to the exposed interior tank wall and the other to each terminal, in turn.

The tester should show 0 volts each time. If the power is off and the readings are not 0, do not touch the heater; refer it to an electrician.

4. Check the reset button. (If it's popped out) Disconnect power to the heater at the main service panel or the switch box and verity that it is off, then push the reset button in and listen for a click.

Turn on the power and wait three hours (yeah, right). If the interior tank wall feels warm near the bottom turn off the power, replace the insulation and access panels and turn the power back on.

5. Testing the high-limit cutoff for continuity. With the power off, label the position of one of the element wires with masking tape, and disconnect it by removing its terminal screws (Yikes!).

With a multi tester set at RX1, touch a probe to each of the cutoff's two left terminals, and then to the two right terminals. The tester needle should sweep to 0 each time, indicating continuity.

If the cutoff shows continuity, test the thermostat; if not, reconnect the wire and recommend the cutoff be replaced by an electrician.

6. Testing the thermostats. Ensure power is off to the water heater.

Turn the thermostat dial counterclockwise to its lowest temperature setting and listen for a click.

If you hear no click, turn the dial clockwise to its highest point, run a hot water tap until the water runs lukewarm, and move the dial to its lowest setting; you should now hear a click.

Label and disconnect the wire to the upper element (Yikes again!). With a multi tester set at RX1, touch a probe to each of the left terminals. The tester needle should remain at infinity.

Then touch a probe to each of the two right terminals on a four-screw thermostat, or to the upper left and upper right terminals on a 3-screw model. The tester needle should swing to 0.

Adjust the thermostat to its highest setting; you should hear a click.

Repeat the two tests; this time the results should be reversed.

To test the lower thermostat, first adjust the upper thermostat to its lowest setting. Then turn the lower dial to its lowest setting; the tester needle should remain at infinity.

Finally, turn the dial to the highest setting; the needle should swing to 0. Of any of your results differ, recommend having an electrician replace the thermostat. If the thermostat tests okay, test the elements. If not, recommend an electrician replace it.

7. Testing the elements. To test the upper or lower element, turn off power to the water heater and test that it is off. Then disconnect one of the thermostat wires (Yikes x 3!).

Using a multi tester set at RX1000, touch one probe to an element mounting bolt or the thermostat bracket, and the other to each element terminal screw in turn.

If the tester needle moves at all, the element is grounded and needs to be replaced.

To test whether the element works, set the multi tester at RX1 and touch a probe to each of the two terminal screws. The tester should indicate resistance in the medium range of the ohms scale; if not, recommend that it be replaced by an electrician.

[homnspector]

Thanks all, #7 is exactly what I was looking for. I knew there was something about the element grounding that had to be checked. I wouldnt normally do this either, but it is nice to know how. I believe the element has to be disconnected to properly measure the resistance as indicated in the last portion of #7.

I think Robert's solution may be easiest but time consuming.

I am also pretty sure only 1 element is on at a time, otherwise, the 30 amp breaker and #10 wiring would obviously NOT be OK for (2) 4500 watt elements.

[Jerry Simon]

I guess what I've been doing and being fooled by is running the heater out of hot water so I can test both elements, turning on the upper one and test using a clamp meter, then turn the upper one back down and then I turn up and test the lower one. With only cold water in the heater, I can then check both elements.

Hmmm...never realized it was one or the other...thanks. But the way I do it, I can check both.

[Chad Fabry]

If the tester needle moves at all, the element is grounded and needs to be replaced.

Uh, if the element is grounded then the wiring is the resistance heater or the breaker has blown.

[homnspector]

"Uh, if the element is grounded then the wiring is the resistance heater or the breaker has blown."

Not sure I understand that?

My thought was that if the element burned out and contacted the side of the tank you would get a grounded reading.

[Chad Fabry]

I guess there could be a high resistance short to ground that would allow the semi normal operation of an element. It would however, result in significantly higher operating temps and/or lack of thermostat control.

If the water is scalding and the thermostat is set low... I guess it could happen. Every element failure I've seen has failed to an open circuit.

[homnspector]

Oh, I understand what you mean now about tripping the breaker. Seems like it would.