I have a very annoying problem with my left ergopower lever
When I push the thumb button to downshift everything is fine, but next time I want to shift into the big ring, the shift paddle moves freely without engaging the ratchet mechanism. I have found, that if I push the shift paddle hard to the left first, it works. It is an all new build - old type Centaur levers.
Be sure that it's not something as simple as a very loose shift cable. The cable should still be tight with the thumb button pushed all the way down, so the chain is in the little ring. The first click of the finger lever should cause the FD cage to move to the right, by a small amount.
The solution depends on whether your shifters are '07-'08 escape models (Centaur and lower levels) or the traditional mechanism used for all other years and models.
There are only a few common problems with the later - broken g-spring or g-spring retainer. The indexing gear can also become worn, but usually only the right side suffers this problem, since it gets lot more use.
If the shifters are the escape model, I've got no clue. I avoided using those.