Had a problem with a Carrier 58PAV070-12 furnace not heating up and flashing LED error code 31. I replaced the glow plug (hot surface ignitor), I replaced the thermostat and added fresh batteries and still no luck. I took out the inducer blower fan to make sure there were no obstructions and to inspect - all was fine. I remvoed the pressure switch and blew into it to make sure the diaphram was still in tact, I also cleared out the hose and pushed throug the small slot where the hose is attached to on the furnace to make sure there were no blockages. STILL NO HEAT!
Finally had an HVAC tech out to the home and he found that upon wiggling the connectors to the furnace control board that he could get the inducer motor to kick on, the glow plug to light up, and finally the burners to start and heat the house. The problem is that after reaching the set temperature on the thermostat the burners would turn off which is fine but they would not light back up even if I increased the thermostat temperature set point. The HVAC tech menitoned that the problem was likely a bad control board. My father-in-law came over to help me tie wrap some of the "suspected" lose connections to the control board which did ignite the burners, but once again, the burners would not light back up after reaching the desired temp.
Thankfully my father-in-law was able to find the identical control board that was in question - part number HK42FZ007. Received it yesterday (December 19, 2011) and installed with my wife's help. We killed the circuit breaker, killed the switch in the garage for the furnace, and turned the gas valve OFF. We then disconnected cables from old control board onto replacement board one by one (but also took detailed pictures prior to doing so that we would not cross any connections). 15 minutes later, the heat was moving through the house!! Tested by letting the termostat reach the setpoint of 70deg which turned off the burners and blower after a few minutes... we then upped the temp to 74 degrees and the furnace worked as expected. The inducer motor kicked on (on this furnace, the inducer motor has a black flywheel fan which is located on the top left hand from the gas valve), the glow plug lit up, the a few seconds later the gas valve clicked on and the three burners were lit. This was an easy fix but just stressful to find the solution. My suggestion is, get a trusted HVAC tech to diagnose, and if you feel comfortable (and no risk to your health or safety), buy the parts and save yourself a couple hundred bucks.
Thanks Dave for ordering the board and thanks Christine for helping me keep the wires straight.
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