I’ve diagnosed this problem and concluded that I need to replace the control board on my nearly 17-year old Carrier 58STA furnace. I’m posting here to ask if others can suggest alternative diagnoses or if they concur with mine. The furnace stopped working recently. I checked the code and found the LED flashing code 31. I confirmed the possible causes of a code 31, and I’m confident none of the fundamental airflow problems that can trigger a code 31 are present, including inspecting the hose leading to the pressure switch. That led me to test the pressure switch. I disconnected the leads from the pressure switch and connected the leads from my multimeter, set to measure resistance (ohms). I confirmed that the switch was open, which it should be with the system off. Several months ago I installed a Honeywell RedLINK wireless thermostat, which is very handy to take with me into the attic. Using the wireless thermostat, I set the thermostat to call for heat. The inducer motor and fan started up right away as expected, after the control board “brain” tested and confirmed that the pressure switch was open. Almost immediately the multimeter showed that resistance through the pressure switch dropped to near zero, confirming that the switch had closed and that the inducer and pressure switch were working correctly. I next inspected the wiring from the pressure switch to the control board. Not much to see there; no visual evidence of any problem. I also used the multimeter to test continuity from the switch connectors to the control board wiring harness connector. Again, no problem. What I examined and tested so far is pretty simple and easy to diagnose. I think that leads to a conclusion the there is a faulty connection somewhere in the control board. Given the vibration to which the control board is exposed, it’s not surprising that a solder joint somewhere on the control board has likely failed. I’ve had that happen a couple times on a flat-screen TV that’s not subjected to anywhere nearly as much vibration as a furnace control board. Another factor indicating a bad control board (solder joint), is that over the last few weeks the furnace has run just fine for several days at a time before again going on the blink. I go into the attic, confirm the code 31 fault (again), wiggle the wiring harness connector, and the furnace then works again properly for a few days until the cycle repeats. So there you have it. But as I said in the opening paragraph, before ordering a replacement control board I’m asking you here on the forum who are more experienced than I to weigh in, please. What do you think? Thanks.

My 11 year old Goodman Furnace GMV950704CX is now not igniting. The blower fan is working, but no heating. In my troubleshooting, [color=#222222]I left the bottom panel off while I flicked the switch and heard the relays click on the board, then the draft inducer kicked into high speed. The igniter is not glowing and after a while, the inducer motor just shuts down. The blower fan will kick in and stay on. I've check the voltage to the igniter and there is no voltage. I noticed the red led is flashing 4 times. From the user manual troubleshooting chart, the 4 blinking led seems to indicate problem with limit circuit or flame rollout limit. I don't understand this code, I would expect the furnace run for awhile and then put this error code. Right now, it is stuck in this state for the whole day and house is getting cold. I've examined the circuit board and see no obvious burns or blown capacitors. I thinking the control board is still the culprit.[/color]