Lack of vapor has two causes, flooding and too dry.
Even though I have no experience with your model, general knowledge would say that it is dry as letting it just sit does not help with flooding.
So, the question is, why is the atomizer dry?
(I am further assuming that it is a catridge+atomizer type rather than a cartomiser type)
Is the cart fill slushy looking? (Fully saturated)
Does the wet cart fill touch the atomizer bridge? (That contact will allow the
juice to wick down to the atomizer coil)
If the fill looks dry get it wet with
juice or change carts. If the fill is not touching the bridge, pull it up so that it will touch when it is assembled.