Performed the level 2 furnace cleaning. I found the heat exchanger full of rust and wear. After using the powder test, I had back draft from the heat exchanger cells. My excess air readings were around 130 which is a little higher than normal but not dangerous. These signs indicate the secondary heat exchanger is starting to wear but hasn’t failed. No moisture coming from the secondary and no CO detected in the air. Recommended we return next year to watch everything. Unit is heating properly at this point.