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Mark Henley
Mark Henley, Journeyman Technician
Category: HVAC
Satisfied Customers: 3217
Experience:  UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential
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Furnace pressure switch open with inducer on. Help!

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Furnace diagnostics indicate "pressure switch open with inducer on." What could be the problem? I recently had my natural gas turned on after being off for a few months. Furnace (Nordyne model KG6RC-080C-16B) used to work fine before, but has not worked since reactivating gas. I don't see a flame in the aperture, nor do I smell the gas. Is there a way to tell that the gas is actually getting to the furnace, or is this not likely related?

No, not related at least not yet. The code means that the vent motor is running but there is no pressure differential being sensed by the pressure switch. The pressure switch is a device like the one in the photo,


If you remove the 1/4" hoses on this and clean out the barbed fittings that the hose (s) attach to you may get it to work, this device is there to ensure that you exhaust vent is clear before firing the furnace.

Customer: replied 7 years ago.
What would you recommend for cleaning the barbed fittings?

You can use anything that has a toothpick shape and won't break off, but you don't want to go past the depth of the barbed fitting when cleaning the pressure switch fittings as there is a diaphragm in there.

Customer: replied 7 years ago.
Okay. I cleaned both ports out thoroughly and restarted twice. I'm still getting the same diagnostics reading--pressure switch open with inducer on. Any ideas?

Yes , the pressure switch is there to ensure that the unit will not fire without sufficient airflow across the heat exchanger basically it verifies that the vent motor is running and that the exchanger or flue is not blocked, the next step would be to make sure that the flue is not blocked. Can you do that?

Customer: replied 7 years ago.
There are 2 White PVC pipes that empty on the side of the house. One is straight. The other is curved downward at the terminal portion & has a mesh filter in it. I looked at both. They both appear free of obstruction, though I can only see up into the pipe that is curved downward.

More than likely you are going to need the new pressure switch.

Customer: replied 7 years ago.
Where would you recommend to purchase a new pressure switch?

A lot of people use this site .

Mark Henley and other HVAC Specialists are ready to help you
Customer: replied 7 years ago.

Thank you very much, Mark. I will order the pressure switch & give it a shot.

Did you need any more information from me regarding the pressure switch? Let me know.

No just let me know how it goes.

Customer: replied 7 years ago.

I ordered the new pressure switch, installed it, and am still getting the same response from the furnace diagnostics--"pressure switch open with inducer on." What is likely to be the problem?

It must not be making the vacuum, can you get the combustion air pipe off of your furnace or at least a portion of it for a test ?

Customer: replied 7 years ago.

I'll sure try. Which is the combustion air pipe?

It will be the one that just dumps into the combustion chamber, where the exhaust one connects to the inducer assembly.

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