Furnace does not light


Old 05-25-10, 02:25 PM
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Furnace does not light

I'm sorry for asking a similar question as many other posts but i could not find one that seemed like the same problem as mine.

My home gas furnace does not light up. I can start the fan and the a/c so I know the thermostat is working. However, when I set the thermostat to heat and to a temp below the present temp nothing happens. I took the cover off the furnace and noticed a switch that is pressed in when the cover is installed. I push the switch with my finger while the cover is off and see a run light on a circut board come on. However the unit never does light up. Gas is on and the unit was working as recently as a week ago. It seems as if everything is working expect that it wont light up and fire the gas.
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Old 05-26-10, 04:22 PM
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Won't light

With the thermostat set for "heat" you need to set the temperature above, not below, the room temperature.
Old 05-26-10, 09:22 PM
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Many furnaces will display a trouble code when they get a heating demand but cannot heat.

Post your furnace make and model.

Most modern furnaces would start the induced draft motor (with heat demand) , satisfy the pressure switch, energize the hot surface or spark ignition, open the gas valve, allow about a minute after igniton to allow the heat exchanger to get hot, and start the indoor fan.

Give your furnace a heat demand, with the door switch depressed, and observe how far it gets. If it will not even try, jump R (24 volt power) to W (heat) at the furnace circuit board.
(It could be as simple as dusty stat contacts)

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