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Old 01-30-2014, 08:11 AM   #1
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Troubleshooting Gas Furnace

I am a homeowner with two nearly identical units, one for 1st floor, one for 2nd floor (Goodman GMS30703ANA). Both units are about 7 years old.

Our 1st floor unit (3 burners) was intermittently failing to ignite (startup sequence made it to the ignitor glowing hot, then failure). Always the same routine: call for heat, inducer start, ignitor light, no flame.

Because our other unit has identical parts, I started swapping: Pressure switch first. Switch worked fine on the other unit. "New" switch installed into the problem unit, and then the problem on the "bad" unit changed: now it will not even start up the inducer. It gets power to the circuit board (red LED light steady red), I can turn on the house fan, but no startup sequence whatsoever (unlike previously when it failed to generate a flame).

So, what are the possible culprits for the original problem followed by the new problem? Which would be the most likely culprit?

I thought: "circuit board". So I swapped circuit boards between the two units (they were identical). Nothing different on the "bad" side; "good" side works fine with the swapped board.

Then, I thought: maybe the ignitor itself. So I swapped that. Same: works on "good" side; nothing different on the "bad" side.

My next guess would be ground wire (inspected it, and nothing obvious wrong with it). I plan to replace it, just in case, but I am ready to call in reinforcements!

I cannot find my multimeter to test anything; decided just to swap potential problems to see if I could hit pay dirt. I've had enough of that and would appreciate helpful suggestions.

If it does not even start the inducer now, while it did previously, what would make sense to explain that new condition?


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Old 01-30-2014, 09:07 AM   #2
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you need a meter and to make sure you got steady 24 volts from W to C when it is calling for heat. may be a bad thermostat. also may be bad grounding if it has that metal plate that mounts the board to the fan. may need more screws in that plate to the fan to keep it tight and that is a common problem. that can blow the board too. or the furnace grounding and neutral may be poor.


"Cut it twice and it is still too short".
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Old 01-30-2014, 11:55 AM   #3
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Thanks, Yuri. I temporarily put in a jumper at the furnace (R to W) to test the thermostat (still can't find my meter!). That got it working. I will remove that jumper and try at the thermostat end to see if it is the wiring or the thermostat itself (I am guessing the wiring--I am seeing some electrical-taped connections from the original installation that look a bit uncertain to me).

I am still puzzled at the original problem--call for heat, startup sequence all the way to ignition glowing, no flame. Since I swapped so many of the possible culprits and they are working on the other unit, I am at a loss for now. I am thinking that the problem will recur, on one unit or the other! Let me know if you have any further thoughts about this.

Thanks again.
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Old 01-30-2014, 04:35 PM   #4
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There should be a flow chart attached to the furnace; for sure it is in your manual. Follow that sequence.

Getting to ignitor glowing hot and induction fan running ...... I hope for you it is in the 24V or thermostat because those darn main boards are expensive.

Two other things that come to mind are the spill over sensor and a faulty sender in the limit. Both of those would have to be an intermittent problem if you are getting ignigtor glow.

They haven't convinced me that I am saving any money with these systems. I can burn a lot of pilot gas for what I've spent on parts.
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Old 02-01-2014, 12:43 PM   #5
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Took off the R/W jumper at the furnace, and connected the R/W wires prior to the thermostat, and it fired right up. So, I decided to hook up a common (C) wire from the furnace to the thermostat to ensure power to the thermostat. Working fine now.

Still do not know what the original problem was. Any guesses?
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Old 02-19-2014, 02:49 PM   #6
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Did you test the gas valve valtage?


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