Posted: 24/09/2014 at 11:47
Pruning is important........correct pruning that is. Often philadelphus is "pruned" just to "tidy it up" thus losing the flowers.
I would be inclined to leave your shrub but perhaps help it along. I would apply potash In early spring. I'm assuming growth is good so would not apply any other fertiliser. Or, if growth is not good then also a general fertiliser a week or two later.
When it flowers next year take the advice about pruning. It's not really difficult. Annual pruning then helps achieve regular flowering.
(I have had fun n games trying to get various stubborn plants to flower...e.g. Laburnum, weigela,,forsythia (all were old and prob seedlings). Success with the laburnum eventually)