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I have a Tempstar natural gas furnace. It has electric element for ignition of the pilot.

It was working fine all December. Now, it does not work as follows: the draft fan starts and runs correctly, then a good looking pilot light comes up. In less than one second, the pilot light turns off and the main burner does not ignite.

I spent a while troubleshooting this issue. I cleaned the pilot sensor with light emery cloth. It did not seem to help. It seems that if I remove two screws holding the pilot light in place and pull it out of the furnace, it does ignite and hold, and if I insert it back into the furnace, the main gas ignites.

I put it back in and everything seems to work. I turn the furnace off, then on, and the pilot stays and the burner lights. Then I went to sleep and again woke up in a cold house.

Overall this behavior seems to be somehow "erratic". As in, things seem to work, then after a while the pilot starts going away again.

Would there be some coherent explanation of this behavior.

Thanks

  • What model is your furnace? – ThreePhaseEel Jan 4 '17 at 12:39
  • Im not familiar with gas furnaces, but this happens on an oil furnace if the burner doesn't get enough fuel either because of bubbles or clogged filter. It may help to verify the flow/pressure at the inlet to the igniter. – aaron Jan 4 '17 at 13:27
  • My furnace is Tempstar NTV6125KJA1 – Igor Chudov Jan 4 '17 at 13:46
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Check to make sure the wiring for the flame sensor is properly connected, and the wire is not damaged. If that all seems good. Replace the flame sensor. If the pilot is not proving, it's almost certainly because the flame sensor is not detecting it.

Flame sensors do go bad, but are typically a cheap replacement. However, it looks like the sensor in your furnace is part of a pilot assembly So it will be a bit more expensive, and a bit more difficult to replace.

  • I would add that I had this problem once after some work was done in the furnace room. The sensor simply had a coating of concrete dust on it, a good wipe down fixed it. Be sure it isn't something silly like that first. – DonBoitnott Oct 23 '17 at 14:21

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