Water Softeners and Corrosion
Naturally soft water has a different chemical make-up to artificially softened water, which has very little affect on the PH level of water.
In the past there was some reluctance from boiler manufacturers regarding the installation of a water softener. However, this situation has now changed, as studies have shown that softened water has no more corrosive affect than hard water.
See following link from Worcester Bosch.