AO Smith Water Heater Error Codes and Troubleshooting

A.O. Smith water heater error codes indicate issues affecting the device’s performance. These codes offer users a quick means of intervention and problem resolution. Understanding these codes accurately is crucial for maintaining the appliance’s optimal functionality.

Codes and Fixes

If the instructions are not clear, contact a qualified person. Electronic Thermostat (ET) and Energy Smart Module (ESM) codes list.

E01 (1 Flash Red)

Dry-fire, electrical power on with the tank not completely full of water.

  1. Turn off electrical power at breaker, add water.
  2. Turn on electrical power at breaker.

E02 (2 Flashes Red)

Water temperature exceeded high limit.

  1. Turn off electrical power at the breaker.
  2. Press the reset button.
  3. Turn on electrical power at breaker.
  4. If error returns call a service technician for assistance.

E03 (3 Flashes Red)

Upper thermistor sensor failure. (Note: Upper thermistor sensor is part of the ET)

  1. Turn off electrical power at the breaker.
  2. Replace Electronic Thermostat (ET).
  3. Turn on electrical power at breaker.

E04 (4 Flashes Red)

Upper element circuit failure. (Note: Lower element is still operable)

  1. Turn off electrical power at the breaker.
  2. Check element circuits for resistance of 5-25 ohms (replace if required).
  3. Check wires at elements and Electronic Thermostat (ET) for damage. If this 4 flashes condition continues, replace Electronic Thermostat (ET).
  4. Turn on electrical power at breaker.

E05 (5 Flashes Red)

Lower element circuit failure. (Note: Upper element is still operable)

  1. Turn off electrical power at the breaker.
  2. Check element circuits for resistance of 5-25 ohms (replace if required).
  3. Check wires at elements and Electronic Thermostat (ET) for damage. If this 5 flashes condition continues, replace Electronic Thermostat (ET).
  4. Turn on electrical power at breaker.

E06 (6 Flashes Red)

Electronic Thermostat (ET) failure (Internal processor).

  1. Turn off electrical power at the breaker. Now turn on electrical power to see if error clears. If error has not cleared, replace Electronic Thermostat (ET).
  2. Turn on electrical power at breaker.

E07 (7 Flashes Red)

Lower thermistor sensor failure.

  1. Turn off electrical power at the breaker.
  2. Check electrical connections at Electronic Thermostat (ET).
  3. Replace Lower Thermistor Sensor.
  4. Turn on electrical power at breaker.

E08 (8 Flashes Red)

Energy Smart Module (ESM) failure.

  1. Turn off electrical power.
  2. Check wires at the interface module for damage.
  3. If this 8 flashes condition continues, replace module (ESM).
  4. See “Overriding The Interface Module (ESM)” by unplugging from the Electronic Thermostat (ET) on page 18. NOTE: Electronic Thermostat (ET) will continue to be operate, hot water will still be available.
  5. Turn on electrical power at breaker.

E09, E10, E11, E12

Electronic Thermostat (ET) error.

  1. Turn off electrical power.
  2. Check wiring at Electronic Thermostat (ET) for damage.
  3. Turn on electrical power at breaker.
  4. If this code flashes condition continues, replace the Electronic Thermostat (ET).

E51

A failure to communicate with the Electronic Thermostat (ET).

  1. Turn off electrical power at the breaker, check all electrical connections, and wiring for damage.
  2. Replace the Electronic Thermostat (ET).
  3. Turn on electrical power at breaker.

E52

Energy Smart Module (ESM) is receiving the wrong data from the Electronic Thermostat (ET).

  1. Turn off electrical power at the breaker, check all electrical connections, and wiring for damage.
  2. Replace the Energy Smart Module (ESM), if this does not correct the problem, also replace Electronic Thermostat (ET).

E71

Energy Smart Module (ESM) thermistor failure.

  1. Turn off electrical power at the breaker, check all electrical connections, and wiring for damage.
  2. Turn on electrical power at breaker.
  3. If error returns call service technician for assistance.

Electronic Thermostat (ET) and Energy Smart Module (ESM)

Electronic Thermostat (ET)
Electronic Thermostat (ET)
Energy Smart Module (ESM)
Energy Smart Module (ESM)

Troubleshooting

No hot water

  1. Check the electric power to the water heater.
  2. Check the upper heating element.
  3. Check the top two screws of the upper thermostat using a non contact circuit tester and confirm that power is off.
  4. Check the resistance of the upper heating element using a multimeter.
  5. Check/Reset Energy Cut Off (ECO) Button.

Temperature Too High

  1. Install or adjust the Thermostatic Mixing Valves for each point-of-use or
  2. Adjust the thermostat(s) on the water heater.

Low Water Pressure

  1. Melted heat traps or dip tube. Soldering copper pipes while they are connected to the water heater can melt the heat traps inside the hot and cold water connect ons or the dip tube (cold water side). Melted heat traps or a melted dip tube can restrict the flow of hot water. If that’s the case, replace the heat traps or dip tube.
  2. Partially closed supply valve. Open the water heater’s supply valve fully.

Water Odor

Harmless bacteria normally present in
tap water can multiply in water heat-
ers and give off a “rotten egg” smell. Although eliminating the bacteria that causes “smelly water” with a Chlorination on system is the only sure treatment, in some cases, the standard anode rod that came with your water heater can be replaced with a special zinc anode rod which may help reduce or eliminate the odor. Contact a qualified person.

Completed Installation

Completed Installation
Completed Installation

Manual Pdf

Gas Water Heater User Manual

AO Smith Troubleshooting Chart

Residential Electric Water Heater Manual

Peter Fuchs
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