no heat from gas furnace


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Old 01-19-10, 12:30 PM
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no heat from gas furnace

a few days ago I noticed my furnace fan was running constantly and it was getting colder in the house. I pulled the front panel off my York gas furnace (approx. 5-6 yrs old) and saw there was a flashing LED on the circuit board which was flashing 4 times each cycle. The 'trouble code' diagram on the panel states this indicates a "high aux. or spill limit switch open". I also noticed the burners were not producing flame and there was no gas smell at the openings. I checked and cleaned the 'ion-type' metal filter plates above the unit although they weren't that dirty ( I had cleaned them only about 3 months ago). This did not resolve the issue. I also unplugged the vaccum hose from the blower housing to the limit switch unit and sucked on the end to create vaccum. I did hear a click of the valve closing when doing this maneuver, so I think this switch is working properly. Any other suggestions?
 
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Old 01-19-10, 01:05 PM
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Limit switch

Usually the sysyem will trip on high limit due to airflow issues. A couple of things to check, is the filter unobstructed and clean, are the registers open and free of blockage, is the evaporator coil clean or dirty.
Another possibility is the blower motor not coming on although you said the fan was running constantly, did you mean the induced draft fan or the blower fan?
If the blower fan is operating it will most likely be the above problems with the dirty evap coil being the hardest to fix / diagnose.
 
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Old 01-19-10, 01:15 PM
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I think the running motor I am referring to is the blower fan motor--it sits under the burner vents and appears to have ducting coming in from above. Where can I locate the evaporator coil?
Also, is there any possible issue w/the heat pump unit outside the house causing any of the furnace issues? We had a helluva wind storm the night prior to the furnace issues, but wind storms are relatively common here and have not caused any problems w/furnace or heat pump function to date.
 
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Old 01-19-10, 02:37 PM
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Did you check any of the limit switches to make sure they closed again? They too can fail, and stay stuck open. Some types can be reset.

Sucking in on vacuum tubes proves nothing useful, since you may be sucking in harder than what the furnace does. Although any issue in this regard, does not sound related to your problem.
 
 

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