100 year old house with 30yo CI boiler

You need a competent professional. I assume this is hot water? Heat loss calculations of the building and calculating the output of the radiators will tell you what water temp you need and what benefit there would be to a mod con. frequently it can be run at lower water temps where a mod con can run efficiently.

EBEBRATT-Ed said:

@FeelingColdColdCold

Try @Charlie from wmass and @New England SteamWorks & @GW

This! You can't go wrong with any of them.

and to answer your question- it aint rocket science. But if you do enough research, you'll maybe appreciate that there's some stuff that takes some skilz. Some plumbers (and i am one) should not be allowed to touch a boiler with a 10' pole.
"there's always someone that can do a job cheaper, and they can probably do it for less money too" 😁