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Remove the burner compartment panel then turn the power off to the furnace wait a minute then turn it back on. Tell me what happens. Does the inducer fan (small fan on the front) run? does the igniter glow? if it doesn't fire up I need to know what the blink sequence is on the control board LED in the blower compartment.
Ok, this is a draft pressure switch (see attached pic for typical) not closing error. This can be cause by a blocked exhaust vent, or the small diameter vacuum tubing to the switch could be kinked or has water in it or the port where it connects to the furnace could be blocked or the tubing could be disconnected. You could also have a bad switch
You need to eliminate the other possibilities first and/or put a manometer on exhaust. Since I doubt you have a manometer just replacing the switch is the cheaper option since manometer is a lot more money than a switch.
The exhaust piping is connected to the inducer fan and runs to outside the house. I doubt any local supply house will sell you a switch since they usually only sell to licensed techs. You can try online by calling these guys. They'll want model and serial number. http://bestbuyheatingandairconditioning.com/contactus.htm
Of course you should always check your electrical connections as well