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How to Inspect a Standing Pilot Light in a Gas Furnace


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Pilot Light Flame Inspection
pilot light and thermocouple

Pilot light and thermocouple

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Pilot Light Flame Inspection
The color of a healthy pilot light flame will look a little different depending on whether your furnace uses natural gas or propane as a fuel. A natural gas flame should be a bright blue with the tip of the flame having just a tinge of yellow. A propane flame should have a bluish green flame with a tinge of yellow at the tip.

To inspect the operation of the standing pilot or pilot light, proceed as follows:

  • Remove the furnace cover panel which should expose the burner assembly and pilot. You should be able to clearly see the flame of the pilot light.
  • If the pilot light is out, attempt to relight it following the instructions found in steps 3 and 4 of How to Light a Gas Furnace Standing Pilot.
  • If the pilot light does not light or does not stay lit, replace the thermocouple as described in Replacing a Furnace Thermocouple.
  • A proper pilot flame should be blue with a yellow tip and strong enough to cover about 1/2 inch at the end of the thermocouple tip.
  • If the flame is too strong and improperly adjusted, it will be blue but may be noisy and lift off the thermocouple causing improper furnace operation.
  • If the pilot light is on but the flame is a weak yellow flame, it will not get hot enough to heat the thermocouple to the proper temperature set point required to allow the gas valve to open.
Adjusting the Flame
There is usually a small screw on the pilot valve body that will adjust the flame. You may have to refer to the manufacturer's instructions to find the screw. Turn the screw as needed to adjust the flame throw.

Fixing a Yellow Flame
A yellow flame is caused by lack of air and incomplete combustion. It can be caused by a dirty pilot tube tip.

Split Flame
This is caused by dirt in the pilot tube. Take a needle or small nail and gently clean the tube.

Flickering or Wavering Flame
A flame that flickers is usually caused by a draft.

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