If a trout boils at your streamer but doesn't connect, try going back to
the same spot with a slower or a more erratic retrieve. The trout might
have thought it stunned its prey, and it's really looking to eat it now. If
that doesn't work, you can try a different fly but in my experience, a
trout that boils at a streamer and doesn't take the same pattern with a
different retrieve will not change his mind just because you changed flies.
Unless the water is under 45 degrees or very dirty and fish are unwilling
to move very far for a meal, it doesn't pay to repeatedly cast a streamer
to the same spot. If you fish a streamer, you should cover a lot of water,
placing your cast in each likely spot and then moving on. Streamers are
bigger flies and that combined with their movement ensures that trout can
see the fly on your first cast.