Armstrong Ultra II 90 furnace shoots out a 3 foot flame when starting


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Old 12-15-11, 11:44 AM
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Armstrong Ultra II 90 furnace shoots out a 3 foot flame when starting

I tried to do a search, but couldn't find anything pertaining to my particular problem.

I live in Michigan. I have an Armstrong Ultra II 90 propane furnace, Model # EG6F80DC12-5. Not sure about it's age, but guessing mid-90's.

I was sitting my living room when I heard the furnace blower come on and then a short time later, I heard an explosion from the basement. I ran down to discover that the furnace door had blown off, but the furnace was running fine.

I shut it off and restarted it with the door off. The blower kicked on and I saw that the pilot flame lit almost immediately. When the gas valve opened, flames shot about 3 ft out of the furnace, then it ran fine. The burner looks fairly clean and once it's running, the flame all looks uniform.

Any ideas?
 
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Old 12-15-11, 12:45 PM
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What you are probably observing is called "delayed ignition."

Do you have a standing pilot light that is lit all the time, or an intermittent pilot that lights each time there is a call for heat?


When the main burner gas turns on, it should light pretty much instantaneously from the pilot burner. If there is a delay in that ignition, there is time for gas to accumulate unburned. When it finally lights --- BOOM!

The usual cause is a pilot burner that is dirty and doesn't extend close enough to light the main burner promptly.

Describe in detail the appearance of the pilot burner flame.

The second most likely cause of the problem are dirty burners.

Is "the fan" you describe the small inducer motor usually located above the burners? Or the fan that circulates ait around the house?

I'm supposing you have an inducer motor that turns on, comes up to speed, causes the pressure switch to close which causes the pilot burner to light and then the main burner to turn on once the pilot burner is lit.

If that's not correct, please describe the sequence of ignition in detail.
 
 

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