Thank you. I think there might have been some issues there because when I disconnected the vent from roof connection and blew on it using a blower, nothing happened at first, but later the motor started spinning. Error 31 cleared. However, error 21 came up. I'm convinced I've erroneously described the situation before when trying to explain what I was seeing. Let me tell you what's happening now: Blower comes on, inducer motor runs, and then surface ignitor lights for 3 seconds or so. Burners never come on. Could it be that the gas valve relay is bad or something? What can I check for? The gas line to the furnace is open and the relay knob is set to on. Thanks...

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Originally Posted by carpet1

Thank you. I think there might have been some issues there because when I disconnected the vent from roof connection and blew on it using a blower, nothing happened at first, but later the motor started spinning. Error 31 cleared. However, error 21 came up. I'm convinced i've erroneously described the situation before when trying to explain what I was seeing. Let me tell you what's happening now: Blower comes on, inducer motor runs, and then surface ignitor lights for 3 seconds or so. Burners never come on. Could it be that the gas valve relay is bad or something? What can i check for? The gas line to the furnace is open and the relay knob is set to on. Thanks...

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Hmmm... limits are good, or no ignition would exist. Thermostat-ok-calling for heat as it shoud. Problem appears to be in igniton. Is gas turned on? At house? At appliance? If so, is there 24VAC across the MV and C terminals of the gas valve (or whatever the two pins are marked). If so, is there gas coming through? 24v and no gas tells you gas valve is shot. If gas is coming through,are the burners clear and clean? Is the flash trail across the burner assembly clear for proper ignition? Is the flame sputtering and dying? If so-clean the flame sensor-replace it if you can as it's probably only about 25USD for a new one or less.

That sounds like quite a bit of work (it's actually not), but that's the trail you'll need to follow to solve this.

Gas is turned on; shares same line as water heater and another furnace. Checked for 24v on the MV and C connections; nothing (checked it before, during, and after inducer motor was running). Checked for 24v on panel on circuit/mother board, where thermostat connects, and good there. Here's something else that's puzzling me; after a couple of attempts to get furnace going, error 31 came back on and inducer motor would not run, then after two or more times, motor would run and error 21 would come on. Anyway, your help is greatly appreciated!

Thank you all for contributing to the resolution of this problem and educating me along the way. The furnace is operational now. The final resolution to the problem was the replacement of the circuit board. I'm not sure how often these go bad, or what caused it, but that solved it. Again, thank you for your assistance...