LsFarm wrote:I've found that if the circulator pumps are run every month, that the cast iron pumps work fine. I've never owned a brass circulator pump. I've had only one pump stick from corrosion, and it sat in pure water for almost a year. I took the motor/impeller off [4 screws] and wire-brushed the housing where it had grown some rust that touched the impeller, and is still running 3 years later.
I'm not a fan of spending 3x the money on bronze pumps when a cast iron pump will work in most cases. However there are exceptions. Yanche has really acidic water and his water system eats parts every few years.
Granted that bronze pumps are more expensive. However cast iron pumps do corrode over time if there is oxygen in the system. I learned the hard way about cast iron pumps in a loop with oxygen. The pumps never seized but when I disassembled the system there were large chunks of corrosion product nearly totally blocking flow. If you have oxygen in the system you also need to use an expansion tank rated for domestic hot water because the less expensive units designed for boilers will corrode and spring a leak within a few years in addition to dumping corrosion products into the system while they are gradually being eaten away.