Q.Non flowering sweet peas
We planted sweet peas some months ago. The plants are growing well on a trellis in a sunny north facing position. The plants are now at least six months old & have no sign of flower buds. What are we doing wrong. They have been watered well. Bryan Green.

Failure to produce flowers is often a sign of excessive nitrogen in the soil. Sweet pea is especially sensitive to this problem because it is in the legume family and can fix its own nitrogen in the roots. It can also be caused by stress from high temperatures.
https://www.gardeningknowhow.com/ornamental/flowers/sweet-pea/sweet-pea-flowers-falling-off.htm
This article is about beans but it's the same idea:
https://www.gardeningknowhow.com/edible/vegetables/beans/get-bean-plants-to-bloom.htm