A.O. Smith Water Heater Error Code 5

Error Code 5 means the water temperature inside the tank exceeded 185°F (85°C) and triggered the ECO, which is the Energy Cut Off safety device. The ECO shuts down power to the heating element to prevent scalding and equipment damage. This is a protective fault code, not a routine status, and requires diagnosis to determine why the water overheated.

The ECO has already cut power to protect the system, so the heater is not actively heating when this code is displayed. You should not simply reset and ignore repeated occurrences of this error, as sustained overtemperature conditions can damage the tank lining, stress plumbing connections, and deliver scalding water to fixtures. If the unit trips this code more than once, stop using it for heating and schedule a diagnostic inspection before resuming normal operation.

The most common causes are a thermostat that has failed in the on position, allowing the heating element to run without interruption, and a shorted heating element that draws continuous power regardless of thermostat control. Sediment buildup inside the tank can also cause localized overheating near the element. Less commonly, a faulty ECO sensor may falsely trip at temperatures below the actual 185°F threshold.

Turning the power off for 10 to 20 seconds and then back on is the first recommended step and may clear the error code if the temperature has dropped to a safe level. However, if the underlying cause, such as a failed thermostat or shorted heating element, is not corrected, the ECO will trip again and the error will return. A one-time reset that holds is acceptable, but repeated tripping requires a component-level inspection.

Repair costs depend on the failed component. A thermostat replacement typically runs in the range of $75 to $200 including parts and labor. A heating element replacement is generally in the $100 to $250 range depending on element type and accessibility. If the ECO itself needs replacement as part of a thermostat assembly, costs are similar. A full service call for diagnosis without parts usually runs $75 to $150, which is often applied toward the repair total.