Furnace Not Working When Temp is Below 50F

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Old 11-02-11, 07:41 AM
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Furnace Not Working When Temp is Below 50F

I have a Goodman GMH80 2 stage gas furnace. It is located in my attic, which is typical for my area, South Carolina. When the attic temp is above ~40 degrees the furnace works fine. When the unit temp drops below ~ 40 it will not ignite. Meter readings across the sensors (that I can find) show continuity. Pressure switch also checks out as OK. Furnace will go through it's normal startup routine (exhaust fan starts & igniter lights) , but at the point where the gas should turn on you hear a click, a small hissing sound, and then no flame. It then goes back to the beginning and tries again for 3 attempts. After 3 attempts Red light just seems to blink continuously. I have tried to warm individual parts up with a hair drier, but with no success. I have even had a repairman come, but it is hard to get them in between 2 and 9 AM on a cold enough morning to see the problem. Any ideas?
 
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Old 11-02-11, 10:13 AM
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Propane or natural gas?

If propane, how large is your propane tank? What other gas appliances do you have?


Please describe the appearance of your hot surface igniter when it heats up.


The gas valve appears to be turning on but the gas isn't lighting. There are a number of reasons that could occur:

1) a hot surface igniter not getting hot enough to light the gas reliably

2) dirty burns or partially plugged burner orifice not allowing gas to flow properly

3) inadequate gas pressure to operate the furnace properly. This can be a problem for with natural gas or propane. With too small of a tank, you can have the propane unable to absorb enough heat to boil the propane into a gas, which can reduce gas pressure.



I'd try using a match on a stick or a gas match to light the gas when the valve turns on which might give you an idea of whether the flames are normal or too small, indicating a pressure problem.
 
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Old 11-02-11, 07:13 PM
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Natural gas.

The igniter glows red hot. It ignites the gas when the temperature in the attic rises in the morning. I guess it is possible that in the colder temperatures it is not getting hot enough. I'll try to use a match and see if it will fire with the extra heat.

When it does fire up there appears to be plenty of pressure across all four burners.

The furnace has operated well for 4 years with only one service call. There is a second furnace that heats the second floor sitting next to this one and there are no issues with it.

The hissing sound only lasts for a second or two. I think it is being shut down by one of the sensor checks.
 
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Old 11-02-11, 10:04 PM
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You need to answer the rest of the questions posed. They are asked for a reason.


Usually a hot surface ignitor should get white hot before the gas is turned on. Red hot might or might not be hot enough.
 
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Old 11-07-11, 11:20 AM
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I finally got back to the attic over the weekend.

I checked the burners and they were clean.

I used a gas match to light the furnace and it fired right up. So the igniter is not getting hot enough to light the gas when the attic temperature is cold.

Thanks for helping. That small comment about the color of the igniter really helped.

Steve
 
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Old 11-11-11, 05:25 AM
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I may have stopped too soon. I order a new igniter and installed it. But, this morning was a cold one and again it did not light.

I was able to light it by hand and the gas pressure seemed very strong.

I'll have to get my meter back out and check to see what the voltage is coming across the igniter and go from there.

Any additional ideas?
 
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Old 11-11-11, 11:10 PM
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