this furnace hasn't been cleaned in at least 12 yrs. i'm hoping that's the cause of all the soot, and why it won't fire. i've changed the nozzle, filter, bled the air. to remove what i'm guessing are the heat exchangers looks very difficult (see pic). is it necessary to open/clean heat exchangers right above the burner, or is it too hot for soot to accumulate so close? does soot start to accumulate at the chimney then build up towards the furnace? from the back end (see pic), i can see buildup on the sides, but they are not completely blocked. i had a tech come out, and i'm guessing he didn't want to clean the thing.
i can upload more pics if necessary.