What Furnace Tune-Up Involves
The tune-up begins with a combustion inspection, checking the burner flame for proper color and shape, testing the flame sensor, and inspecting the heat exchanger for cracks or corrosion, since a compromised heat exchanger can allow combustion byproducts into the living space. We also verify the venting is clear and drafting correctly, since a blocked or improperly sloped vent affects both performance and safety.
From there we check the ignition system, whether it is a standing pilot, hot surface igniter or intermittent pilot, and test the safety controls that are meant to shut the furnace down if something goes wrong, including the limit switch and flame rollout switch. These components rarely get attention outside of a scheduled tune-up, since a furnace that starts and produces heat can still have a safety control that is not functioning correctly.
We clean the burner assembly, check gas pressure against the manufacturer's specification, inspect the blower motor and belt if applicable, and change or clean the filter. Static pressure is measured to confirm the duct system is not restricting airflow beyond what the blower is designed to handle, and every reading is compared to the manufacturer's specified range before the visit is complete.