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davewolf 11-18-2006 01:33 PM

gmp100-3 furnance won't try to ignite
i have a goodman gmp100-3 furnace and it does not try to ignite. I get no heat. It worked last season. I set the thermostate for heat and blower motor comes on, but it doesn't try to ignite and i don't smell gas.

aczer 11-18-2006 01:50 PM

perhaps your igniter
A couple of days ago, my furnace did not ignite either. I got the manuals (on line) for my thermostat, my furnace, and the control box inside the furnace. On one of the troubleshooting charts, there was an indication to check the resistance of the igniter using my ohmmeter - which revealed that the igniter had infinite resistance, hence it was defective. The igniter is a hot surface which has replaced pilot lights. Once I got out the old one I could see instantly where it was broken (after 15 years).
The new igniter cost me $58, and only took a few minutes to install. I also found out that you should never touch the working surface of the igniter because the grease on your skin will ruin it.
Now, your problem may be different. In my case, the controller shut off the gas flow very rapidly when the igniter did not heat up, and the blower never started at all.
Anyway, that was my one experience with a nonstarting furnace. Good luck.

davewolf 11-18-2006 02:07 PM

i checked the resistence and it was not infinite.
the ignitor could be ok

ponyracer 11-18-2006 02:40 PM

Thanks Aczer! I have the same trouble, fans on but no heat. I checked the ohm reading on the igniter and it is OL. I kinda assumed that this would be the trouble but found this site during a search to make sure. Where did you find the manuals and such online?

thanks again:thumbup:

aczer 11-18-2006 03:23 PM

if the ignitor is ok...
follow the wires from the ignitor that lead to the control box.
my control box had about 6 or 8 wires coming off of it, going to the ignitor, the blower, and goodness knows where else.

shut off power to the furnace, and then, while you are looking at the control box, turn the power back on. you may see a red LED turn on briefly and go out, which is supposed to indicate that the electrical wiring is OK. if it stays on, that is supposed to mean the control box is bad, and if it blinks that means the control box thinks something external to itself is mis-wired.

when I turn on the power, my control box blinks once. if the thermostat is set to heat, I can hear some clicking in the furnace, then I see the bright orange glow of the ignitor, then I can hear a low woosh of gas, and then the flames start and the ignitor goes off.

I just did internet search for the manufacturers of each component. The control box led me to a troubleshooting flowchart in a PDF file.

aczer 11-21-2006 02:13 AM

By the way, I found that sometimes you get the best results if you just search the internet using all or some portion of the part number, rather than the name.

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