Electrolysis

David Ashton

I have a situation in an older Radiant floor heating system that is as follows.

The floor tubes are Solaroll EPDM, with (6) 3/16" tubes in the mat. We use a 40% propylene glycol mixture in a closed loop system. The boiler is a Power Vent Model HI-B by Hydrotherm, 85,000 BTU.

All cold water supply piping, and return HW piping is copper; however the outgoing riser above the boiler is galvanized. The boiler is cast iron, to which an 1-1/2" galvanized pipe rises up 3' or so then turns and supports an expansion tank on its way to return HW to the slab. The relief valve supporting the expansion tank then connects to a brass piece which connects back to the copper supply line. Enclosed are several photos.

We've sprung a leak in the galvanized pipe at the nipple where it connects to the expansion tank relief valve. I am told that galvanized pipe has a electrolytic reaction to cast iron and black pipe. I know it has a reaction to copper, but didnt know about black and cast.

Is it true that the galvanized will react with the cast, and that it will also react with the glycol?

Since I need to fix the leak, if I replaced the riser in copper, how would I connect the copper to the cast iron tank to stop electrolysis? How would I connect the copper to the expansion tank relief valve to stop electrolysis?

Any advice? Thanks very much