I've been inspecting our 1920's cast iron radiator hot water system which uses 1 1/4 and 1" galvanized piping. The system was refurbished around 5 years ago, with new vents and a new on-demand boiler but the original piping is almost entirely untouched.
Several of the radiator valves are leaking or broken and I started a discussion on potential replacement of those here:https://forum.heatinghelp.com/discussion/170978/radiatior-valve-replacement-1920s-cast-iron#latest
While inspecting the system over the weekend I found several other areas with occasional drips from corroded joints and this has me concerned about the piping that I can't see. If I close the makeup water valve for the system then the boiler will shut down with a low pressure warning within a few days (going from ~12psi to under 7).
The house is 1920's with decorative plater/lath ceilings on the main level (which I don't want to touch) and a finished but very old basement which is going to get renovated at some point. Total sq ft on the main floors is ~2000, with around 11 radiators in all.
We love the radiators and heat and I'm wondering how other folks have dealt with this scenario. At one extreme I can continue to repair leaks as and when I find them - at the other extreme I've seen all of the piping replaced with a manifold and PEX piping.
PS. My local Ontario plumbing/heating firm quoted $ CDN for replacement of the valves and $ to replace a small section of corroded pipe (which I ended up doing myself - and yes, 400l took a long time to drain and refill!).