Furnace Pilot Light


  #1  
Old 10-15-02, 05:29 AM
dookie
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pilot light

I've shut off the pilot several times this year because of useing Kilz in the house. The pilot was out for about a month and I suspect that moisture releated problems are plaguing it. The furnace is a 1986 Snyder General gas furnace with Honeywell gas control valve (VR8200H 1012). The flame was small (11/2 "),did not overlap the thermocouple very much and was blue with a deep blue interior and yellow fringe. Turning the adjustement screw located beside the pilot tube on the control valve as I continued to hold down the pilot button seemed to have little to no effect on the flame characteristics. The pilot would not stay lit. I disconnected the burner unit to clean the pilot burner and reinstalled it and replaced one of the two electrical contact leads to the control valve (it was making poor contact). The pilot now adjusts with the screw, but is very large and has a hissing sound except when adjusted to a large flame. The pilot still will not light. Also I measured across the thermocouple (valve end) while the pilot was lit and found the resistance changed as it was heated. It appears I'm getting too much gas or too much air at the pilot tube and have another problem such as a bad thermocouple. Is there something I should do to change the characteristic of the pilot flame? How can I check the thermocouple?
Thanks
Dookie
 
  #2  
Old 10-15-02, 07:06 AM
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Welcome Dookie to my Gas Appliances forum and the Do-It-Yourself Web Site.

If you did not enlarge the pilot orifice, accidentially or intentionally while cleaning it, the flame should encircle the thermocouple only. The tip of the thermocouple should be in the pilots top 1/3rd of the flame. The thermocouples tip should be glowing cheery red in color.

If all that is correct, chances are the thermocouple is wornout, weak or dead. Replacing it should resolve the problem.

If not, it's possible the magneto is defective. The magneto part is the part that the thermocouple screws into. It can be screwed out and replaced on many types of gas valves.

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  #3  
Old 12-01-02, 07:33 PM
dookie
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pilot light

Thanks Tom:
I replaced the thermocouple, pilot tube and orifice for $36 and it lit on the first try! The flame color also changed to a blueish green in the interior, surrounded by lighter blue and then by yellow. The flame also adjusted with respect to size.
 
  #4  
Old 12-01-02, 08:02 PM
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Hello and Welcome back dookie

I see you found your original question and used the reply button. In doing so you kept the entire thread together for easy reading and following along.

Gald to know you we able to correct the problem. Hope my reply helped.

The part about the yellow in the pilot is of concern. There should not be any yellow in the pilots flame. The other colors are correct and glad you included them.

The fact that you mentioned replacing an orifice removes that possiblity from the list of possible reasons for a yellow flame. To adjust the flame to it's correct size, it should encircle the thermocouples tip.

The tip of the T-Couple should be in the top 1/4rd of the flame and not in the center. The center is not the hotest part of a flame. The outter end is the hotter area because it is exposed to the air which the center is not. Hence the color difference.

A new T-couple will perform well if heated but for not as long a time if incorrectly heated. The correct pilot flame size is important.

Correct pilot flame size not only provides enough heat to the T-couple to allow it to produce it's full rated current, it also provides a positive source of burner ignition.

If the flame has yellow in the tip, it is adjusted too large or there may be dust on the orifice or in the primary air opening to the pilot. The primary air opening is either on the pilot assembly or in the tubings securing nut, etc. There may be two air openings or one funnel shaped opening.

If the is any doubt about dust or lint in the air openings, a can of computer cleaning compressed air can be use to clean or clear out the dust. Just be positive the pilot flame is extinguished and the assembly is cooled before cleaning. The spray is flammable!

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