What is often the initial step in diagnosing a furnace issue related to combustion air supply?

The initial step in diagnosing a furnace issue related to combustion air supply is to test the air intake. This is critical because adequate combustion air is necessary for efficient furnace operation. If the air intake is blocked or restricted, it can lead to inadequate air supply, resulting in poor combustion, increased emissions, and potential safety hazards. By checking the air intake first, a technician can quickly determine if a lack of combustion air is contributing to the furnace issue.

Addressing other elements in the combustion process, such as the gas line pressure or vent blockages, while important, usually comes after ensuring that the air supply is adequate. Measuring temperature differentials is also diagnostic but typically applies to evaluating system performance rather than directly investigating combustion air issues. Thus, confirming the status of the air intake is a pivotal first step in troubleshooting combustion air supply problems.