What action is required if CO levels in an appliance exceed 100 ppm during testing?

When carbon monoxide (CO) levels measured in an appliance exceed 100 parts per million (ppm) during testing, it is essential to complete an appliance clean and tune. This is because elevated CO levels can indicate improper combustion or exhaust issues, which can be addressed through maintenance activities such as cleaning the burner, adjusting the fuel-to-air ratio, and ensuring proper ventilation and flue functionality.

By performing a clean and tune, you can restore the appliance to safe operating conditions. This process also helps to identify any underlying issues that could contribute to poor combustion and elevated CO levels, ensuring the appliance operates efficiently and safely after maintenance.

In contrast, replacing the appliance immediately may not be necessary and could be a costly step without understanding the root cause of the high CO levels. Reporting to local authorities is also not typically the immediate course of action during testing unless there are specific regulatory requirements or immediate danger present. Lastly, re-testing alone would not resolve the underlying issues and may lead to repeated safety hazards if the appliance is not cleaned and tuned first. Therefore, the requirement for an appliance clean and tune is the most effective and appropriate response in this situation.