A. O. Smith Water Heater Error E02 – Causes & Fix
The tank water got hotter than the safety limit, so the ECO cut power to both elements – reset it once.
Safety first · Consult a professional
This heater runs on 240 volts. Switch off its double-pole breaker and confirm the power is dead before removing any access panel, and don't touch element terminals or wiring. Water in the tank may be far hotter than normal – check it at a tap with a thermometer before anyone showers, and never cap or plug the temperature-and-pressure (T&P) relief valve.
- Unplug the appliance or switch off the breaker before opening any panel. Mains voltage can kill.
- Hot surfaces and hot water can cause burns. Let the appliance cool down first.
At a glance
Severity: Moderate
- Meaning
- Water Temperature Exceeded High Limit (ECO Trip)
- Typical repair cost
- $0–$500
- DIY difficulty
- Moderate
E02 is a code from A. O. Smith's residential electric tank water heaters that use an Electronic Thermostat (ET) with a front-mounted Energy Saver Module (ESM) – it is not a gas appliance, and A. O. Smith's gas, tankless and heat-pump lines use different code tables. The ESM shows E02 with a flashing alert icon (the ET's LED gives two red flashes) when the water has exceeded the high limit and the ECO (energy cut-off) has opened, removing power from both heating elements. A. O. Smith's manual gives the owner procedure: breaker off, press the ECO reset button on the ET, breaker back on, and call a technician if the error returns. The reset restores heat, but something made the water overheat – most often an element shorted to the tank or a thermostat relay that stuck closed – so a repeat means a repair, not another reset.
How it looks on the display
Model families & display variants
| Model family | Shows | Note |
|---|---|---|
| Electric models with Energy Saver Module (ESM) display | E02 | Displayed with the alert icon flashing on the front module. |
| Electronic Thermostat (ET) diagnostic LED | 2 flashes | Two red half-second flashes, then a pause, repeating – visible behind the upper access panel or when the ESM is unplugged. |
| Heaters from the same family sold as State or American | E02 | If your heater has the same ET/ESM control, the code should match – confirm with the manual for your model number. |
Symptoms
- Energy Saver Module shows E02 with the alert icon flashing
- ET diagnostic LED flashes red twice, then pauses
- No hot water, or water cooling off, after a period of unusually hot water
- T&P relief valve discharge pipe wet or recently discharged
- Breaker hasn't tripped – the heater simply stopped heating
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Heating element shorted to the tank (grounded), so it keeps heating even when the thermostat switches off
- Relay in the Electronic Thermostat stuck closed or ET control failure
- Upper thermistor (part of the ET) reading too low or losing contact with the tank
- Loose or overheated wire at an element or ET terminal
- Set point at maximum combined with a very long heating cycle or power disturbance
- ECO itself weak and tripping early
Fix it step by step
Check the water temperature safely
Before anyone uses hot water, run a nearby hot tap and measure with a kitchen thermometer. A. O. Smith's own scald chart shows 140°F water can cause serious burns in under 5 seconds, so warn the household if it's very hot.
Look at the T&P relief valve
See whether the discharge pipe from the relief valve is wet or dripping – a sign the tank overheated or overpressurized. Leave the valve alone and never cap its pipe; mention it to the technician.
Tools: Flashlight
Cut power at the breaker
Switch off the water heater's double-pole breaker. If you have a non-contact voltage tester or multimeter, confirm there's no power at the heater before going further.
Tools: Multimeter
Press the ECO reset button
Remove the upper access panel, fold back the insulation and leave the plastic guard in place. Press the red ECO reset button on the Electronic Thermostat until it clicks, then refit insulation and panel.
Tools: Screwdriver, Gloves
Restore power and watch one heating cycle
Turn the breaker back on and check that E02 has cleared. After the tank has finished heating, measure the tap temperature again: it should be close to your set point (A. O. Smith suggests 120°F to reduce scald risk).
If E02 returns, stop and call for service
A repeat trip means a component is letting the water overheat. A licensed plumber or appliance technician checks each element for a short to ground, tests the ET relays and inspects the wiring.
How to reset E02
- Turn off electrical power to the water heater at the breaker.
- Remove the upper access panel and press the ECO reset button on the Electronic Thermostat.
- Refit the insulation and panel, then turn the breaker back on.
- If E02 comes back, leave the power off and call a service technician.
Where the parts are
- 1Flue
- 2Fan
- 3Heat exchanger
- 4Ignition electrode
- 5Gas valve
- 6Circulation pump
- 7Expansion tank
- 8Pressure gauge
- 9Temperature sensor
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| ECO reset (owner, per manual) | Yes | $0 |
| Replace grounded element yourself (drain, element wrench, new gasket) | Yes | $25–$60 |
| Element replacement by a plumber | No | $180–$350 |
| Replace Electronic Thermostat (ET) | No | $250–$500 |
| Repair burned wiring or terminals | No | $120–$250 |
Rough US estimates; technician call-out fees vary by region. Not a quote.
When to call a technician
Call a licensed plumber or appliance technician if E02 reappears after one ECO reset, if the T&P valve has discharged, if you see scorched wires or melted insulation behind the panel, or if you're not comfortable working around 240-volt equipment. Replacing elements or the Electronic Thermostat involves live-voltage testing and draining the tank.
Frequently asked questions
Why do I have no hot water at all after E02?
The ECO cuts power to both elements when the high limit is exceeded, so the heater stops completely until the ECO is reset manually. That's a safety design, not a second fault.
Can I just keep resetting the ECO?
One reset is what the manual allows. If E02 returns, a part is letting the water overheat – often an element shorted to the tank – and continued resets expose you to scalding and rely on the T&P valve as the last line of defense.
Is E02 on A. O. Smith the same on gas water heaters?
No. This E02 belongs to the electric models with the Electronic Thermostat and Energy Saver Module. Gas, tankless and hybrid heat pump models use different codes, so check the manual for your model number.
What temperature should I set to avoid another E02?
Set point alone rarely causes E02, but 120°F is a good balance of comfort and scald safety. If it trips at a moderate setting, the control or an element is at fault.
Sources
- Official A. O. Smith user documentation and support pages (facts only; wording is our own)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy