I have a Rheem UpFlow RGPJ-07EAUER. Noticed it was not working when room temp was well below set point. Went down staris and looked at the furnace and it was doing nothing. Except for a very small faint humming. Looked at the lights on board. (One Green "OK" LED, and one yellow "Flame" LED)
Green light comes on and stays on.
Yellow light never attemps to come on and stays off.
Changed out the board, and also the inducer motor. Inducer motor still does not come on. Is this the first thing that should happen once I set the set point and turn the heat on? I never notice the ignitor coming on or flames at all in the unit. I am pretty confused and any help would be appreciated.

Yes combustion blower should start first. If you have a voltmeter check to see if you have power to the blower.