Almost the same question was asked about a week or so ago. I cut mine back hard in the autumn and it has flowered very well this year. I'm not too fussy with the pruning as long as you cut back to any sort of bud it will thrive. My two are are cut back to about seven foot each year otherwise they will become enormous. It might just be the characteristics of your specimen. Have a look at how to produce cuttings and perhaps ask an owner of one of the trees that flower well for a couple.

Thanks, I have always cut mine back in late spring, I wonder if that has made the difference!

A few other things can reduce bloom:
Lack of direct sun can keep the bush from building up enough energy to bloom, so check that buildings or shade trees aren't blocking off more than half of the available sunshine.
Lack of phosphate or potash can hinder bloom, too. Sometimes a dose of tomato food is helpful.
Too much available nitrogen makes the plant want to put it's energy into growth, rather than bloom. Reducing applications of high nitrogen fertilizers, such as blood meal or fish meal, can help. That may be hard to manage if the bush is next to a lawn, since lawn food is high in nitrogen, too.

Hi Stu,
I cut my Black Beauty back quite hard late last summer and it has grown and bloomed very well this year. I also have a sambucus Nigra Black Lace as I heard that I would get more blossom and berries if I had two or if a wild common elder was growing nearby. I am about to cut the B Lace back hard and sacrifice the berries this year and it should make enough growth to bloom again next year. The black beauty has larger berries so I will leave those for the birds and prune it when the leaves have fallen. I don't know whether this is the right thing to do but over the three years I've had them it seems to have worked here..

I cut my Black Lace back after flowering and it has always flowered well. I do have a common elder as well.
The berries are very small and puny and not worth keeping, especially as the wild one berries well.

I'm wondering Stu....you live in the North East if I'm not mistaken, so you probably have similar winter and growing season to me on the East Coast of Scotland. Now I don't think we need to cut things back quite as hard as those further South as they don't have such a long time to grow and ripen again. I cut mine back in the late winter, but I don't do it as the books say right to the ground. I only cut them back once they have reached the height I want, and only back to about 2 feet high at the very shortest. Usually I don't cut them back more than by a half. This year I really went for it on my Sutherland Gold and it has taken until now to show any real shape and won't have any flowers at all. Lesson learned :)

Sambucus don't grow into trees very quickly from my experience. In my last garden I left it alone, never pruned it apart from branches which overshadowed other plants, and even after several years it was only about 8 feet tall.
The one I have here is growing much more quickly (and has black fly!) but I want it to grow higher than the fence which it's in the process of doing - in three years it's put on about 3ft.

I normally cut mine back in early spring but I'll try cutting back in autumn. In the past I cut it down to two buds about 3ft from the ground.