fault code for a centurion heating system

I have a centurion heating system model gf9s06012up11j that is a couple years old. It just stopped producing heat. I see that there is a fault code of three red flashes. (Pressure Switch stuck open). What does this mean and where is it so that I can unstick it? Also ! the basic info on the sheetmetal cover talks about a reset switch for the history of warning codes. Where should that reset be?

Not knowing your system, it sounds like you have a draft inducer blower for the flue. In that type of system, there is a pressure switch to monitor pressure in the outlet of the blower....we don't wan't the gas burner coming on if the blower is not running. Follow a small piece of vinyl tube from the blower volute...it will lead to the pressure switch . Sometimes it can be cleaned. Maybe just replace it.