Heating Help

non ferrous circs for non-oxygen barrier radiant?

Recently isolated a 1990's butyl rubber radiant system from the boiler using stainless HX.  Original Grundfos 15-42 cast circs were still running, two now have failed - old boiler was a electric thermal storage unit - 800 gallon tank.  Will new cast circs (grundfos 15-58) have a chance of living a long productive life as the 15-42 did or should we insist on using stainless circs?  Now that the circs are the only iron part on the radiant side of the HX, will they degrade faster?

Oxygen

Oxygen will deteriorate the cast iron circulators on the radiant side if the tubing is non-barrier.  Replace them with bronze or stainless steel.