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Saturday, October 31, 2009

No Furnace Ignition

I need advice on how to fix a furnace. I have a Suburban 24,000 BTU furnace that won’t do anything when called on by the thermostat. I can’t hear the gas being called on or even the blower. I am sure I have checked all of the fuses. Everything else is working fine, stove, refrigerator, oven and air conditioner. The furnace is in an Itasca.
Robert, (Garden Grove, CA)


Robert, first thing to check is the voltage at the furnace. Be sure you have adequate voltage at the furnace itself. Likewise, be sure the ground connection is secure. Next, at the furnace also, disconnect both blue wires going to the wall thermostat and short them together. If the furnace now ignites, you have a faulty thermostat or a broken wire leading to it. 

If still no action, leave the thermostat wires shorted together and check for voltage at the printed circuit board. If voltage is present going into the board, it is probably a failed circuit board. The board can be bench tested to determine if it is faulty. Most professional repair facilities will have the board tester. It's also possible the relay in the furnace could be faulty, but we would need the schematic or wiring diagram to fully evaluate that possibility. My guess, though, is that you are experiencing either a voltage/ground problem, (hopefully), or the board is faulty, (hopefully not).

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