Boiler with a repair plate

1938 house. Peerless Steam Boiler, oil, 2002
Any idea what happened here?
Thank you
Looks pretty nasty for a cast iron boiler that’s only 16 years old

Certainly poor on going maintenance issues with rust in the sightglass. There used to be a tankless coil, it leaked for a long time to have that much corrosion. Coil has been removed and covered with a blank plate. I see new rust on the blank plate, corrosion on the cast iron flange likely. You can’t treat equipment like crap and expect it to just keep going. Protect yourself and defer it to the HVAC technician.

Mark, that’s great, thanks for your help.