Performed the level 1 furnace safety check. Heat exchanger looks okay, no cracks located. However, it did fail the smoke test. After the combustion test was done, we determined the issue is in the secondary heat exchanger with usual wear and tear. Combustion readings were higher than normal, but, nothing dangerously high and no CO detected in the air. Recommended we return anually for inspections and cleanings. Unit is heating properly and safely at this time.