I found LP condensing gas furnace working when I arrived. Customer said furnace quit running about three different times during the very cold weather in the past three weeks. I found exhaust pipe cut in furnace room!! Most exhaust is dumping into basement. I tested for carbon monoxide in home. 1 ppm. Someone suggested cutting pipe a couple years ago because if ice build up at vent termination outside under the deck.(See picture) I checked venting under the deck. I found short-circuiting exhaust is icing up the intake pipe! Exhaust vent needs to be extended to end of deck. I taped exhaust vent back together as temporary repair until proper coupling can be installed and vent termination corrected. I also removed cap from burner box for temporary service. Also, combustion blower motor is very noisy. housing vibrates.