I have a 10 years old Carrier 58PAV070-12 furnace with a problem. The blower comes on, but it never ignites. It is giving me error code 12 first, then 31. My understanding of that code 31 has to do with the venting of the furnace or pressure switch. I did some troubleshooting myself already. I tried cleaning up the pressure switch, the rubber tube going to it. I also tried taking the two wires off pressure switch and jumper them together when the inducer motor is running, still no ignition. There doesn't seem to be any air blockage on the unit. What am I missing here? Anything else I should have checked? The pressure switch seems to be working fine, motor inducer is running, no blockage, filter is clean, any suggestions? Could it be something to do with the ignition heating element? Please help, Thanks much!