I am a highly skilled home service professional who recently completed a furnace inspection at a client's home. During the inspection, I noticed that the air filter needed to be changed. I checked the air filter and found that it was 16 X 25 X 1. I also noticed that the system had thrown a water circuit open code, but it did not affect the operation of the unit. I cleaned off the flame sensor and verified that the amperage was good. The client stated that they would change out the air filter on their own.
