Assuming the motor will turn in both directions (which implies the pump is working correctly):
Something jammed in the check valve of the helm?
If you look at the back of the helm unit, there's a couple of biggish hex heads towards the bottom. Removing these reveals a couple of spring-actuated check valves that are the overpressure releases (i.e. if you crank the helm to the stop, then keep going, the check valve opens and allows fluid to leak through, preventing a blown seal or hose or whatever.) It's apparently possible for debris to jam the valve open, which essentially overrides the stop.
If that doesn't seem to be the problem, repost, and I'll see what else I can come up with.