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oolowrideoo 10-25-2009 01:48 PM

Help with furnace diagnostic code
I just replaced the single stage thermostat on my Comfortmaker 9MVX furnace with a Honeywell VisionPro IAQ multi-stage system. I flipped the dip switch in the furnace to use a 2 stage thermostat, but whenever there is a call for the second stage heat, the diagnostic led on the furnace flashes 9 times indicating: High Pressure switch open when should be closed. Any advice on how to fix this?



gregzoll 10-25-2009 02:29 PM

Did you follow the steps to program the thermostat to recognize the type of Furnace/Air Handler it is hooked up to? Also, did you double check the wiring to make sure connected properly.

Plumber101 10-25-2009 03:00 PM

The problem you are having has nothing to do with the stat.

You moved dip switch 3 to ON or OFF?

You made a connetion to W2 on the control board?

You can go to and go to technical and look upi the instruction man to diag flash code 9

On 2 stage furnaces with comfortmaker there is two pressure switchs

oolowrideoo 10-25-2009 03:26 PM

I previously did all of these things... My next step was to check the actual pressure switch. Turns out, I must have accidentaly knocked the hose loose running to the switch. I re-attached the hose, and everything works great. Thanks for the quick replys!

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