E18
A.O. Smith
Line Voltage / Power Supply Fault
A.O. Smith water heater shows E18; unit may not start or may shut down intermittently
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Incorrect supply voltage, Loose power connections, Faulty transformer (on low-voltage models), Control board power supply failure
How to Fix / Troubleshooting
Safety: Turn off power at the breaker before inspecting electrical connections.
- 1. Verify supply: Confirm the heater is connected to the correct voltage circuit (typically 120V for gas, 240V for many electric models). Use a multimeter if qualified.
- 2. Inspect wiring: Check the junction box on top of the heater for loose wire nuts, burnt insulation, or signs of overheating. Tighten connections and replace damaged wire.
- 3. Check breaker: Ensure the breaker is not tripping repeatedly. If it is, there may be a short or overload that needs professional diagnosis.
- 4. Transformer (if equipped): On models with a separate low-voltage transformer, test output voltage. Replace the transformer if it is not providing the correct voltage.
- 5. Control board: If supply voltage is correct but E18 persists, the control board's internal power supply may be defective and require replacement.
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Repair Difficulty
Medium
3/5
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