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How to troubleshoot electric water heater 

Troubleshooting requires basic electric knowledge plus screwdriver and multimeter
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How to diagnose water heater electrical problems
Top thermostat with terminals numbered <> see larger image


top thermostats


Interior diagram water heater top thermostat
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diagnose water heater problems
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Overview of causes
Gradually less hot water: Sediment or lime build-up in tank, shorting wire, shorting breaker, bad lower element
Suddenly less hot water: Lower element burned out, bad upper or lower thermostat, loose wire, shorting breaker
Overheated water or lukewarm water: Bad thermostat, element shorted > read testing steps below
Suddenly no hot water: Red reset tripped, circuit breaker tripped, bad upper element, bad thermostat, loose wire

Quick answer: Red reset button tripping:  > problem can be bad upper or lower thermostat > shorted wire > or  shorted element > or thermostat temperature set too high > or insulation covering thermostat removed. Troubleshoot steps are below. Quick fix without testing: replace thermostats read how, inspect all parts for signs of high heat and burning, tighten all screws very tight against copper wire, re-install insulation and covers and see if problem persists.

Quick answer: Water heater has electricity but not heating water: 240V water heater must receive 240V from circuit breaker. Check tank label for voltage of appliance. If circuit breaker is burned or broken, water heater receives 120V, so heater appears to have electricity but is not working. Use multimeter to test water heater for 240V at L1-L3 screws on upper thermostat -or- test breaker  [listen for crackling sound of shorting breaker].  Other causes: red reset button tripped, top thermostat bad, top element burned out, loose or shorted wire: read troubleshoot steps below.

Quick answer: Water visible around base of water heater? > element leaking > tank rusted beyond repair and ready to rupture > thermostat not sitting flat against tank > thermostat set high or insulation missing and TP valve releasing pressure > bad TP valve <> rusted tank needs replacement before rupture > Read: water heater is leaking

Also read how to use multimeter


Troubleshooting Part 1: Review ECO red reset button and tank safety features 

Red reset button or 'high limit control' or Energy Cut Off or ECO will cut off electric power to entire water heater if water reaches 180° F <> or if electrical short causes top thermostat to overheat. 

ECO shuts off both hot wires in the 240V circuit. Look at diagram on left: 240V arrives at L1 and L3 screws of top thermostat <> when ECO is tripped, L1 and L3 screws are hot but electricity stops there.

Understanding safety features: Residential electric water heaters have 3 critical safety features: <> 1. Circuit breaker that cuts power at service panel <> 2. TP valve see image that releases water if pressure builds inside tank <> 3. ECO red reset button that turns off electricity when overheating is detected.

TP valve and ECO prevent water heater explosion. In physics, hot water expands and puts pressure on container holding water. Metal tank will rupture violently if water gets too hot. ECO is first line of defense. The next safety device before water heater explodes is a properly functioning TP valve that releases scalding water to floor through ¾” pipe.  

ECO red reset button is tripping: 3 causes

1. ECO will trip when either upper or lower thermostat sticks in ‘on’ position causing continuous heating. Once water reaches 180° F, the ECO trips and turns off electricity to entire water heater.

2. A loose wire or electrical connection inside thermostat -or- between parts will trip ECO.
Loose wires generate heat, causing high resistance. ECO senses heat from bad connection and trips. Not every loose wire will cause ECO to trip, only those that cause top thermostat to overheat.

3. Bad element shorted to ground near center of element will trip ECO.
When element is shorted to ground near center of element, the short does not draw enough current to trip circuit breaker. By design, a thermostat only turns off 1 hot wire, but a 240V water heater has 2 hot wires. If short does NOT trip breaker, then 120-volts flows to ground through half of element, continuing to heat water until ECO trips.

Troubleshooting part 2: Test ECO red reset button

Electricity is 'on' during this test. Caution needed since 240-volts can kill or injure you. 

Call licensed plumber or keep reading.

Protect yourself: Tape multimeter leads to wood paint sticks so hands do not get near electricity see image

Water heater must be on dry surface and not in water. A wet water heater or water heater that was flooded is dangerous >> turn off power. YES Use adequate lighting. YES Wear dry tennis shoes and dry clothes. YES Stand on dry boards or several layers of dry cardboard. DO NOT lean against or touch metal pipes or metal ductwork. DO NOT stand in water or on damp surface. DO NOT stand on bare outdoor soil or metal ladder. Do not hold metal screwdriver in your mouth. Put down dry boards and plywood so your body does not conduct electricity to ground which will cause serious injury. 

1. To get ready. Turn off electricity to water heater. Open hot water faucet so cool water enters tank. Remove covers on water heater see image so you have access to thermostats and elements. 

2. Turn electricity back on so you can test parts. 

3. Set multimeter to read 240 Volts AC see image.

4. Test L3 to T2 and then L3 to T4. Then test L1 to L4. If voltage is present with any test, then EOC is not tripped, so move forward to next section.

5. If voltage is NOT present then ECO is tripped and requires resetting. Water in tank must be cool. Push red button to reset. If ECO will not reset, then replace upper thermostat with new one from hardware store. How to replace thermostats  If ECO resets then move forward to next section.

Troubleshooting part 3: Test the Elements

Electricity is off during this test. Look for loose screws and burned wires see image. Burned wire is caused by loose screw or element shorted by sediment or lime build-up inside tank. Cut back burned area of wire. Continue testing elements.

1. Disconnect wires from both elements see image  

2. Set multimeter to read Ohms > or use continuity tester from hardware store see   

3. Test-A: test across the two element screws with multimeter and resistance should read about 12.8 Ohms for 240-Volt 4500-Watt element. For 30 gallon tanks with 3500-Watt elements, reading is about 16.4 Ohms. see chart with formula
If you are using continuity tester instead of multimeter, the light turns on when element is good, but element must pass next test too.

4. Test-B: test each screw to any bare metal part of water heater. If the multimeter reads any Ohms at all, or if needle moves even tiny bit, then element is shorted and needs replacement with new one purchased at hardware store see how. If you are using continuity tester instead of multimeter: if bulb turns on or flickers or is dim then element is bad. How to replace element 

Use same wattage for replacement element. End of element marked with wattage. Also label on side of tank shows wattage. Tank wattage is element wattage since both elements are never 'on' at same time. See image

Troubleshooting part 4: Test top and bottom Thermostats

Electricity is 'on' during this test. Wires are attached to elements see

Attach wires to elements. Start with cold water in tank. Set multimeter to read 240 Volts AC

1.Turn on electricity to water heater. Cold water in tank means upper element will be on read how a water heater works

2. Test L3 to T2 and it should read 240V > test L1 to L4 should read 240V.  This means upper thermostat is sending power to upper element. Then test across both screws on upper element. If element does not show 240V, and you know element is good from Part 3 test, then one of the wires between thermostat and element is shorted and needs to be replaced. 

3. While upper element is on, check for electricity going to lower thermostat and element. Test L3 to T4 should read 0-Volts. If  L3 to T2 and L3 to T4 both read 240V at same time, then upper thermostat needs to be replaced.

4. Once upper thermostat is satisfied, then L3 to T2 should be 0V and L3 to T4 should read 240V. This means electricity is being sent to lower thermostat and element. 

5. Test lower element screws to any bare metal part of water heater. Test should read 240V. If there is no voltage, then wire from top is shorted and needs to be replaced.

6. Ready to test lower thermostat. Keep in mind that lower thermostat turns on and off frequently to maintain temperature in tank. Test lower thermostat by testing lower element. Test across both screws of element and it should read 240-Volts. If bottom element never shuts off, or if ECO trips before lower element shuts off, then lower thermostat is defective. Replace lower thermostat with new one purchased at local hardware store.

7. If lower element is receiving electricity from top, but never turns on <> then replace lower thermostat. If lower element still does not turn on, and you know it is good, then one of the wires from top are shorted and need replacement.

How to replace thermostats

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