No it doesn't sound like it needs to come apart, if you can actually see the flap is attached, and where you put the cable on the arm for it to move is ok, then moving the control should move it, unless it has become detached at the control mech.
Defo not a take out heater job, it's just the movement at the control is not being transfered to the flap bit, so investigate the control next.
tabetha