I am trying to find out why a gmp100-3 furnace does nothing. I have not yet tried anything except open covers. The control board has not led on, does this mean it is shot or could there be another problem. Any answers to this problem would be great. (live in cleveland, getting cold :) at night)

First make sure the power is turned on to the furnace and the thermostat is calling for heat.

Next check the blower safety switch since when the panel is off the furnace will not work anyway. This little switch does go bad so I suggest you test it to make sure it is good before going further.

If your unit has a circuit board there should be a fuse on it so check that after you test the blower door switch. Post back with results.

I have power to the switch, from the switch and to the circuit board. The led (red) still not on. Fuse is good, even replaced it.Connected therm wires red/white together,still nothing. I called repair service, and they want $100-00 just to look at it, price includes first half hour. Another place said furnace being in attic may incure a $75.00 extra fee. Seems like a ripoff.

If you have power to the board (110/120)Volts and the light is not on with all the other stuff you checked I would say it has to be the board.

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Originally Posted by hvac1000

If you have power to the board (110/120)Volts and the light is not on with all the other stuff you checked I would say it has to be the board.

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Should there not be 24v to the board? Might it be a bad transformer?