# Primary Limit circuit open



## thiesnm (Feb 3, 2009)

My furnace is running but it isn't pumping out heat. The primary limit circuit open light is blinking. Do I need to call a furnace guy or is this something I can fix myself.


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## beenthere (Oct 11, 2008)

Need to find out what it causing it to open.

Hopw are your air filters.


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## thiesnm (Feb 3, 2009)

The air filter was in backwards and it is dirty and it is kind of deformed. Like blown out.


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## beenthere (Oct 11, 2008)

That may have been the cause.
When I need to change out a limit, I find the cause, and then after correcting that, and replacing the limit. I check to make sure I was right, and have the caused fixed.
Need to check temp rise after replacinga limit.


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## thiesnm (Feb 3, 2009)

What exactly is a limit?


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## beenthere (Oct 11, 2008)

Is this case.
It should be your temp limit.
It got too hot, too many times.

When it gets to X temp, it opens to shut off the burner to protect the furnace and your house.
When it cools, it closes again.
They re a safety device. So they aren't made to cycle the burner all the time. So after opening too many times, they tend to stick open.


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## thiesnm (Feb 3, 2009)

so how do you close it?


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## beenthere (Oct 11, 2008)

You don't.
You replace it.
Its now unreliable.


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## dac122 (Sep 5, 2008)

been is right so make sure you find the cause instead of just replacing it. A worst-case scenarios is a cracked heat exchanger.


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