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Don park is the dealer of rheem, try to call them and find the parts you need.

That means the t-stat is OK. You should check the ignition park for the solution.

Which model of keeprite furnace you use now and based on the light flash means something wrong with the flame sensor.

no. what type of humidifier you use right now? Check whether the drain pipe is blocked?

How did you know the problem is caused by pressure switch? You should call the service guy, the pressure problem could be caused by inducer fan, broken pressure switch, blocked vent or wire...

Black-Rh, white-W. for now, only for heating is OK. You should replace the signal wire, if you replace a new furnace or want to control fan.