That does not seem to strange to me considering all the UN-insulated steam piping I see in these pictures. It is criticle to insulate those pipes. You will need to use fiberglass, as rubber will just melt. Talk about a waste of heat.
Does that radiator that hisses all the time ever heat up? If ye and you see no steam coming from it, leave it alone, but I am willing to bet is either not open enough and not heating properly or is a defective valve.
I stumbled on this yesterday, and after looking at your picture of your boiler, you may want to check this out. It is a recall for that vent damper you have. Picture looks exact. Here is the link
Gas Vent Dampers Recalled by Effikal Due to Carbon Monoxide Hazard