Panel Radiator

We retrofitted a geothermal heat source into an existing house. Many of the existing floor areas had polybutylene tubing in the slab for the radiant heat. In any new areas, we used a barrier pex. One small area had a concrete floor and no tubing. We installed a steel panel radiator by Buderus. In about a years time it sprung a leak. Apparent cause was corrosion. conclusion is the polybutylene tubing must be letting Oxygen in. The entire system is either pex or non-ferris metal like copper. Assuming this was not just a bad radiator, but really was affected by the lack of barrier, I need to find out if there are any panel radiators made out of non ferris metal? Can anybody help?
George