Two possibilities - You say north side of your house, does the plant get some sun or at least bright light? While most benefit from some shade, too much shade can reduce flowering.

More likely is cold weather in your zone. Most H. macrophylla cultivars flower primarily on previous years growth. Damaging weather includes early fall freezes that take place before the plant is completely dormant, extremely low winter temperatures, and late spring freezes that occur after the plant has broken dormancy. In zone 6, the most damaging weather is usually a late spring freeze that kills the flower buds - to avoid this you would need to protect the plant until after danger of hard frost.

Another possibility: If you are fertilizing them: Stop!
Just add an application of compost in the fall and spring.
If you have a nearby lawn area and you fertilize it, you could be getting runoff and since lawn fertilizer is high in Nitrogen(N), it is promoting lush, green foliage on your Hydrangeas, at the expense of blooms.

FWIW, some macrophyllas are just cranky and refuse to bloom!
I have an old 'Glory Blue' that is about 25 years old and once it stopped blooming for about 10 years.
I had a serious talk with it and promised that it was headed to the compost pile the following year, if I saw no flowers. The following year it produced some huge blooms and has bloomed every succeeding year since then! True story!

Not fertilizing it either. I'm going to leave it alone this year, and if it doesn't bloom, its getting cut off at the ground and round-up'd.

Sounds like a wonderful plant worth saving. North side is kinda the wrong place for it...unless it got morning sun in days of yore. Move it to a place where it gets morning sun. Move it now and you might get flowers. Sounds like a monster to move, but might be worth it. And don't roundup...dig it out. That stuff is nasty.

Unless it shaded by overhangs (deep eaves) or other, much larger plants, the north side of a structure gets a lot of indirect light in the northern hemisphere and even some direct sun in midsummer. I have a lot of hydrangeas in a mostly all shade (but not heavy shade) on the north side and they still bloom profusely. I'm not at all sure that's the issue......I'd be much more inclined to think the hydrangea is suffering from cold damage to its flower buds in zone 6, unless you are providing winter protection.

FWIW, in zones below 7, that is the primary reason Hydrangea macrophylla fails to bloom -- provided incorrect pruning is not the issue, which it appears not to be.