It is usually meant to shut the product down when not enough burning fuel is detected from the last burner in the gang of burners inside the furnace.
Bad flame sensor goodman furnace.
The flame sensor monitors the burner to detect whether or not a flame is present.
The furnace lights but then shuts down after a few seconds short cycles the porcelain on the flame sensor is cracked.
If the flame sensor is defective the furnace may not heat.
Most people have their furnaces in a basement or laundry area where there is excess dust in the air.
The flame sensor is sooty or corroded.
How to tell if flame sensor is bad.
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However a more common reason is that it is just dirty.
The flame sensor monitors the burner to detect whether or not a flame is present.
As with any piece of equipment a simple reason could be that dirty flame sensor just goes bad.
The easiest and most cost effective fix is to clean the flame sensor with steel wool or a green pad.
The flame sensor is constructed out of metals that will create an electrical current if in the presence of a flame.
Since your furnace is still having what sounds like flame sensing problems i would suggest making sure the flame sensor is positioned in the flame where it is getting a good hot blue flame to sense.
It is a sensitive sensor so any type of dust or carbon buildup could cause it to malfunction.
This will cause the furnace will shut down quickly when it s being turned on and will fail to give the heat to the entire house.
How to know if you have a bad flame sensor is quite easy to diagnose.
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Just enough to remove the build up.
If the flame sensor is defective the furnace may not heat.
The flame sensor is just one of those safety measures.
I would suggest checking all connections to make sure they are tight especially the ground connection on the transformer.
To know if the flame sensor is in a bad condition it will not sense the flame even the furnace is running properly and a flame sensor will automatically shut down a furnace unit.