Split level single unit heats downstairs but not up?

[2K2 LS1]

OK long story short we have one unit for both floors. Horrible design in my mind; but hey it's what they built the house with. The 1st floor heats just fine; however the 2nd floor doesn't. The T-stat shows heat and On but there is no heat coming out. Could it be the blower fan or something else? Were would one suggest a minor-DIY'er start investigating before calling the HVAC guys out?

[Venom]

There is a flap on the plenum that controls the upstairs heat. Check to see if it has power and is functioning properly.

[2K2 LS1]

There is a flap on the plenum that controls the upstairs heat. Check to see if it has power and is functioning properly.

Thanks VENOM....I will do that this afternoon.

[2K2 LS1]

I reset the panel in the attic near the unit and we are back in business.

[Venom]

Too easy. I'm glad you got it figured out.

[2K2 LS1]

Yeah I watched the upstairs and downstairs unit cycle a couple times and noticed the heat indicator led wasn't coming on when the upstairs unit would come on. I knew it should be calling for heat and it should then cause the red heat indicator led to light up but it wasn't. I figured it was a communication error between the t-stat and the panel so I said what the hell and gave it a shot. I reset it and bam! back in business lol