Step 1: Conduct a Visual Inspection

First, the system is set to "heat," the thermostat is turned up and the fuel-jets are checked to make sure that the fuel-burning process is properly initiated.

After turning off the power and fuel supply, the specialist conducts a visual inspection of the venting system (Image 1), which is designed to remove flue gases. Venting ducts are checked to make sure they are in good condition and well sealed, and joints are checked. Each joint should be sealed using at least three metal screws (Image 2).

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Step 2: Remove the Covers and Check the Filter

The furnace cover and blower-compartment covers are then removed (Image 1) to inspect the mechanical parts and check the filter.

The filter is removed (Image 2) and checked to see whether it needs replacing. The filter shown in our demonstration was an older style filter.

Typical filters slip into a slot in the air-handling portion of the furnace. They are marked with an air-flow indicator (Image 3). It's important that the filter is installed so that it is oriented properly, with the arrow pointing in the direction toward the furnace.

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Step 3: Check the Blower

The technician uses flashlights and some specialized mirrors to check the condition of the blower to make certain there are no obstructions. For some furnaces, the blower motor is lubricated periodically.

Step 4: Remove and Clean the Burners

The burners are then removed from the furnace (Image 1) for cleaning and to provide better access for a visual examination inside the furnace. The inside of the furnace chamber is inspected for defects including rust, holes and separated seams.

The burners are cleaned (Image 2) using fresh water to remove any dust and debris. This will ensure safer and more efficient burning.

The sensor and pilot is cleaned (Image 3) with a wire brush and an emery cloth. This will help ensure that these devices operate effectively.

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Step 5: Reassemble the Components

The components are then reassembled and put back into the furnace.

Step 6: Perform Safety Tests

The "high limit" on the furnace is checked to prevent overheating, and the gas meter is clocked (Image 1) to check the rate of fuel usage. The final safety test is to check the flue products for carbon monoxide levels -- using a carbon monoxide meter (Image 2) -- to be sure that the furnace is burning cleanly.

Safety Tip: It's highly recommended that you invest in a carbon monoxide alarm (Image 3) for the inside of your home. This will alert you if potentially dangerous carbon monoxide gas levels get too high in your living space.

Safety Tip: Keep the area around the furnace clean and unobstructed for safety and accessibility.

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