A.O. Smith gas water heater displays E05 and shuts down; unit may overheat or cycle rapidly

Safety: Turn gas control to OFF and disconnect power. Allow the tank to cool completely before resetting or servicing.

• 1. Reset high limit: On some models, the ECO is integrated into the gas control and resets when power is cycled. On electric models, there is often a red reset button on the upper thermostat behind the access panel. Press firmly until it clicks.
• 2. Check temperature setting: Ensure the thermostat is not set excessively high. For most homes, 120°F (49°C) is adequate and reduces scald risk.
• 3. Flush sediment: Sediment can cause localized overheating. Connect a garden hose to the drain valve, shut off cold water supply, open a hot faucet, and drain several gallons until water runs clear. For heavy buildup, perform a full flush.
• 4. Inspect thermostats/sensors: On electric models, remove power, open upper and lower access panels, and verify the thermostats and high-limit switch are firmly against the tank. Replace any thermostat or ECO that shows signs of burning or cracking.
• 5. Gas control replacement: If the ECO in the gas control has tripped and will not reset, the entire gas control valve/thermostat assembly must be replaced.

If E05 recurs frequently, contact a technician to check for stacking, recirculation issues, or a defective control.