Q.Fruit On A Young Pear Tree
I have a 6 year old conference pear tree with three main branches coming off the trunk, two were covered in leaf and flower, the third was slow to come into leaf and not a single flower on it.

Certified GKH Gardening Expert
Unfortunately, your photos did not come through. It sounds like one of the branches below the graft point was allowed to grow out. This is part of the root stock, and not part of the scion.
These branches from the root are, usually, more vigorous than the top scion. This means that it will likely kill your scion at some point, and should be removed.
Since this is one of the main branches, I would do this during dormancy.
https://www.gardeningknowhow.com/edible/fruits/pear/pear-tree-pruning.htm
When pruning, make sure to remove the fruitless branch and keep all new instances from the lower portion of the tree from forming. These growing from the rootstock will likely never fruit.