Carrier 58SXB furnace error code 31
To clean the trap you need to remove all lines to it and run hot water through the open ports. I'm not familiar with this model, but this is how I clean the traps on other Carrier High Efficient models. If there is a buildup of reddish-brown "sludge" in the trap I would suspect the secondary heat exchanger is plugged, or soon to be plugged. In this case, pull the blower and look up inside the furnace, into the secondary HE. All you should see is metal. If you see any reddish-brown build up on the surface (sometimes it kind of looks like tiny worms coming through the surface) then your secondary HE is plugged AND rotted out. It could still be plugged even if you don't see this, it just means that the fins haven't eaten through yet. Going any further than just a visual inspection should be handled by a pro, as you really need to know what you are doing. Call Carrier, and they will most likely put you in contact with a company that knows what they are doing.