paint coming off Hardie siding

We have a new home that is six years old. After two years paint started coming off in spots on the west side of the house. This is the side that gets most of the wind and rain. The contractor repained the spots. The paint is S/W paint with a 30 year warrenty. They say if they used the wrong primer, on warrenty.
We are still having problem. What does the contractor need to do to correct the problem???