Carrier Furnace Plugged secondary?

[Plumber69]

58MVP100-20* What would cause this to the secondary heat exchanger. I believe the unit is 8-12 years old.

 

[Plumber69]

58MVP100-20* What would cause this to the secondary heat exchanger. I believe the unit is 8-12 years old.

 

[Sponsor]

 

[Stuff]

Running propane with wrong orifice? Burners mis-adjusted/overfiring?

 

[Dana]

What Stuff said- most likely running with insufficient excess combustion air. With condensing burners they can't use too much excess or it will lower the dew point of the exhaust for less combustion. But running without enough can result in soot clogging.