When vapor meets liquid, it can condense. When gas (NCG) meets liquid, it can dissolve. When there is too much gas in the liquid, it can either evolve slowly at a wall or at the surface ... or it can come out explosively.
Drop-wise or film-wise condensation of a pure vapor exhibits some of the highest heat transfer coefficients possible. But add a little noncondensible gas (NCG) and those coefficients can drop by orders of magnitude.