intermittent main burner

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  #1  
Old 03-23-04, 04:27 PM
rizzo
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main burner intermittent Carrier GS

Hello to all.

I have a Carrier GS furnace circa 1991 that fires the main burner successfully, but the burner will go out when the unit is cold. The burners are restarted by the still burning pilot almost immediately. This cycle is repeated several times until the firebox is warmed up. I have found I can prevent this flame-out by adding some additonal heat to the pilot sensing element via a propane torch via startup. I have thus far checked the electrical connections for tightness and cleaned the pilot sensing element (that leads to the ignition lockout module PC board) with an emory cloth, both to no avail

Though some of the experts here might be able to suggest possible solutions.

thanks in advance!
 
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  #2  
Old 03-23-04, 08:50 PM
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Hello: Rizzo

Chances are the element you are heating is the prover. It sense the heat from the pilot flame and allows the burners to fire up. Cleaning it may correct the problem. Best to remove it, clean it with steel wool and replace it exactly as it currently is.

May also be a flame sensor, which does the same function for the burners. Senses burner flame. Hard to say exactly which element it is based on the description.

Assumption is the pilot is ignited by a spark ignition system (IID) Which means an Intermitten Ignition Device. The sparking ignitor lights a pilot flame, than the flame heats the prover element. Than the burners fireup.

If that is the sequence, cleaning or replacing the element should resolve the problem, based on the problem description and how I am reading it. Hope this helps.
 
  #3  
Old 03-25-04, 03:36 PM
rizzo
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resolution

Wanted to post the resolution to this problem for the benefit of forum readers. The bi-metallic strip in the pilot assembly had worn out and only worked if excess heat was applied. THe diagnostic give-away was an intermittant voltage drop on the wires leading to the pilot assembly. This voltage drop, when received by the ignition lockout module, cause the main burner valve in the gas valve to shut down.

Thanks for the feedback, it's nice to have heat again.
 
  #4  
Old 03-25-04, 04:43 PM
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Hello: Rizzo

EXCELLENT diagnostics, well detailed and explained.
Glad you where able to fix it yourself too.

Thanks for posting back the update solution. Many others will learn by it.

Pilot flame sensor bi-metallic strip in the pilot assembly was the culprit... Something to remember if you care to help others.

Regards
Sharp Advice
 
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