Seems daft and doubt it has any scientific basis but my mother moaned about her wisteria never having flowered and someone said about the rice pudding. She made one from scatch and dug it into the soil (yuk) and it flowered the very next year!
Seriously I think it is quite common for them to take up to 8 years to flower.
Make sure you keep it well watered. We have 2. One is prolific - the other has only started flowering this year. It got cut back hard last year after been watered regularly. Seems to have rewarded our interest in it.
I have one and it flowered the year after planting. I've been advised that their roots need to be extra deep, as they like to be really cold and suffer if not planted deep enough when the weather is hot and heats up the root. If the plant is already established, you can try and remedy this by putting slate or bricks round the base to keep the roots cool!
My neighbour followed the 5-bud/2-bud advice, and her flowers are prolific this year. Hers is three years old, she had it as a new-house gitt when she moved in.
Go out, stand next to it, and threaten it. Say " If you don't flower next year, your'e firewood !".
My father had an old Cox apple tree which had never fruited properly, and he did that. The following autumn he had to prop up the branches with old brooms and clothes props, the crop was so heavy.