Electronic gas water heater displays E04 and shuts down; unit may have overheated or cycled frequently.

Safety warning: Overheat conditions are serious. Turn off power and gas. Allow the heater to cool completely before touching any components.

• 1. Manual reset (if equipped): Some American Water Heaters models have a manual reset high limit switch behind the access panel. Press the red reset button firmly until it clicks. If it immediately trips again, do not continue resetting.
• 2. Check thermostat setting: Verify the temperature setpoint on the gas control valve or electronic control is not set excessively high. For most homes, 120°F is recommended.
• 3. Inspect flue and draft: Ensure the flue baffle is correctly positioned and the vent is not blocked. Poor draft can trap heat in the combustion chamber.
• 4. Evaluate for scale buildup: If the heater is older or in a hard-water area, heavy scale on the tank bottom or heat exchanger can cause localized overheating. Listen for popping or rumbling during operation. Flushing the tank and, for condensing models, descaling the heat exchanger may be required.
• 5. Test temperature sensor: On electronic models, locate the tank thermistor(s) and check resistance against the temperature chart in the service manual. Replace if readings are out of range.
• 6. Gas control valve check: If the burner continues to fire beyond the set temperature or cycles erratically, the gas control valve/thermostat may be sticking and must be replaced by a qualified technician.