I don't know much about those in particular, but a lot of flowering bushes are like this... wrong/no fertilizer and they don't bloom. Try one made especially for blooming.
The balance of nutrients can be really important. Takes a lot of oomph to make those flowers.

Lj - can you try the east side of the house? I think they say north side because then you won't get as much intense sunlight, later in the day. I think they need the more gentle light, but don't quote me. I'd try east, see how it does, if not good then try somewhere else. I keep moving plants until they die or thrive.