AO Smith E02 Error: Upper Heating Element Circuit Open
Troubleshoot AO Smith electric water heater code E02 (upper element open).
The electronic thermostat board detects an open circuit (infinite resistance) through the upper electric heating element, often caused by element burnout or dry-firing.
Probable Causes
Upper heating element burned out due to age or mineral scale encrustation.
Dry-fire condition: power turned on before tank was completely purged of air and filled with water.
Loose screw terminal lead or burned wire connecting upper element to thermostat.
Diagnostic & Testing Steps
- •E02 error code shown on electronic thermostat digital screen.
- •Water heater provides lukewarm or no hot water.
- •Upper heating element fails to draw amperage under call for heat.
Tools & Equipment Required
- ✓Digital Multimeter (Resistance & AC Voltage)Measure upper/lower immersion heating elements (12 - 14 Ω for 4500W at 240V; 0V before touching).
- ✓Non-Contact Voltage Tester (NCVT)Verify zero voltage at upper thermostat lugs before touching any electrical terminals.
- ✓1-1/2 inch Water Heater Element Socket WrenchUnscrew threaded screw-in immersion element from water heater tank bung.
- ✓Phillips #2 & Slotted ScrewdriversRemove upper and lower access panel covers and fold back fiberglass insulation.
- ✓Heavy Absorbent Towels & Catch PanCollect residual water when removing heating element from drained tank.
Fast Reset Sequence: Universal 5-Minute Power Isolation Reset
Before unmounting panels or beginning diagnostic procedures, attempt this manufacturer reset to clear transient microcomputer lockouts:
- 1.Press the Power or Cancel button to interrupt the active cycle.
- 2.Completely unplug the appliance or trip the dedicated wall circuit breaker.
- 3.Leave disconnected for 5 minutes to discharge internal power supply capacitors and reset microcontrollers.
- 4.Reconnect power and run a test cycle to confirm whether the error is transient or hardware-related.
- 1
Step 1: Verify Zero Voltage at Upper Element
[ ] DoneRemove upper cover and test for AC voltage across element screw terminals and to ground.
Verification:Multimeter confirms strictly 0 VAC present across all terminals. - 2
Step 2: Measure Heating Element Ohms
[ ] DoneDisconnect one power wire from element and place multimeter probes across the 2 screw posts on 200Ω scale.
Verification:Healthy 4,500W element measures 11.5 Ω to 14.0 Ω; replace if open circuit (OL) or shorted to tank ground. - 3
Step 3: Refill Tank Completely Before Powering On
[ ] DoneInstall replacement screw-in element with new rubber gasket, open hot water faucets until water flows free of air, then restore breaker.
Verification:Tank is completely filled, E02 clears, and water heater heats water to setpoint.
Repair Solutions
Turn off 240V breaker and remove upper element protective cover and insulation.
Disconnect power wires from element and measure resistance across the 2 screw terminals with digital multimeter.
Standard 4,500W element should measure approximately 12.8 Ω. If multimeter reads infinity (OL), replace element.
Frequently Asked Questions
What causes a water heater dry-fire?
Energizing the 240V breaker before the tank is completely full of water causes the element to heat to 2,000°F and melt within 30 seconds.
Can I replace a 4,500W element with a 5,500W element?
Only if the wiring gauge (10 AWG) and circuit breaker (30A) are rated for the higher continuous current draw.