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Old 01-15-2012, 08:59 PM   #1
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Open Pressure Switch?


Lennox 80MGF

My flashing LED indicates an open pressure switch. Where is this switch and does it need replacement or just resetting? It also indicates that it could be a blocked condensate drain. (I am not familiar with the location of either of these) Any ideas/thoughts? Thanks.


Last edited by Hauffhouse; 01-15-2012 at 09:19 PM. Reason: Added model #
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Old 01-15-2012, 09:17 PM   #2
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Open Pressure Switch?


The pressure switch will be a round container (2-3" across) with one or more hoses attached to it. It will be in the same section of the furnace as the gas valve/burners/inducer vent motor.

The open pressure switch Led fault code means that the pressure switch that was supposed to close during the heating cycle but did not.

The easiest possible cause for it not closing is because the hose to the pressure switch is split or there is a debris build up in the opening of the pressure switch or at the other end of the hose inside the inducer motor hose port.
A straightened paperclip or very small screwdriver is a good tool to explore if either port is obstructed.
Let us know what you find?

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Hauffhouse (01-16-2012)
Old 01-16-2012, 07:39 AM   #3
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Open Pressure Switch?


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Originally Posted by Hauffhouse View Post
Lennox 80MGF

My flashing LED indicates an open pressure switch. Where is this switch and does it need replacement or just resetting? It also indicates that it could be a blocked condensate drain. (I am not familiar with the location of either of these) Any ideas/thoughts? Thanks.

this "code" is simply letting you know that the pressure switch did not close. Normally when the furnace is not running the switch is what we call "normally open", when the t-stat calls for heat and the draft motor starts it pulls the pressure switch closed, this MUST happen for the ignition sequence to be completed.
Several things can keep the pressure switch from closeing.....if the ventor motor does not start, the pressure switch will not close, if the flue pipe of even the throat of the ventor is plugged the pressure switch will not close. If the proving tube (usually connected to the draft motor housing or the burner box is plugged or obstructed the pressure switch will not close.......finally and the rarest situation.......the switch its self is bad.
Typically a trained service technician will use a magnihelic Gage and or a manometer to determine the root of the problem.
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Hauffhouse (01-16-2012)
Old 01-16-2012, 11:46 AM   #4
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Open Pressure Switch?


Problem has been fixed and furnace is running just fine. Thank you for your reponses/help.

Happy New Year!
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