hot water radiator system - additives?

JPL

Hi, all… Was hoping to get professional opinions on this. I have a cast iron Weil McClain CGA7 boiler, about 20 years old. The heat emitters are both cast iron radiators and cast iron baseboards. Over the years, the system has been drained and refilled, perhaps 10 times. This was due to replacing/adding heat emitters, changing to a primary/secondary loop, adding zones, etc. Over the last two years, the boiler has started making noise — the hotter and more it is cycling, the noisier it is.

I've purged to make sure it is not air trapped in the heat exchanger, so I think it is probably calcium build up. I've seen additives on the market which are supposed to address this. But think I have heard they are not a good idea and could lead to more problems down the road.

Any thoughts? I'd hate to have to replace a boiler that is otherwise working, but realize that if left unaddressed, the problem could evolve into something more serious in the future.

Thanks!