My carrier condensing gas furnace (model number 59SP5A040E141110) was shutting down and flashing code 31 which indicates that 'pressure switch did not close or reopened'. Since everything had been working fine since it was installed in 2012, I assumed it to be a problem with condensate drainage. The drain ran through a condensate neutralizer which was very dirty and preventing sufficient water flow. I removed the neutralizer. Everything then worked fine for about a month. Then it started flashing code 31 again. I removed the condensate trap inside the furnace and cleaned that out as it was also pretty dirty. It was still giving me problems. I started tweaking with the z tube (i think that is what its called) that sends condensate drainage outside of the furnace and then into the condensate pump. And when I say tweak, I mean very minor, very slight movements of that tube that seemed to drastically increase or decrease water flow. Found a good position for it and water was steadily flowing out. Worked fine for about 5 days. Now its flashing 31 again. Water still flows out of the z tube while the unit is running but doesn't seem to be enough to prevent the 31 code from coming back. Any other ideas as to what might be causing this 31 code to come back? I should also add that I disconnected the hoses connected to the pressure switch and the condensate trap to make sure they weren't clogged.


Any help would be greatly appreciated. Thanks!

 

Have you check the vent pipes for blockages?

 

Trkky removing the trap & flushing well with hot water. You could also have a restriction where the hose attaches to the furnace.