I have an old Peerless steam boiler in the hose I've been living in for the last 5 years. I have made improvements to the unit as the technicians who service it recommended periodically. At the end of last winter, they had me relace the low water cutoff. The boiler was asking for too much water and they said the "float" in the old water cutoff was shot. It was a few hundred buck to buy and replace it. I just turned my heat on for the first time yesterday. After 2 hours running, radiators started leaking and I could hear boiling water in them as well. There were some banging noises too. I shut the heat. This morning I checked the glass water level indicator and it's filled to the top rather than half - where I was always told it should be. Any ideas?

The fill glass on a steam boiler is never to the top because the boiler needs head room to create steam. You probably have a problem with the boiler fill valve allowing too much water into the boiler.

NOTE: if you do not know what you are doing with a steam boiler call a pro for a on site inspection and repair. To dangerous to play with.