bryant boiler having water leavel problems

Dan_42

Hi, I’m still trying figure this boiler out. I have owned the house since 2000. The boiler has never really given me much trouble. I replaced the safety control on the gas main and nothing more. I made sure all the radiators were pitched properly, no hammering. The only odd thing was the water site level was always hard to read, when I would add water it was never straight forward. I would have to add a little and wait for a moment before I would get a true reading. For the first 4 years I never or almost never filled it with water. Now in this cold spell it seems like every other day. Yesterday I must of overfilled the boiler and water came raining out from the bottom I thought the boiler was cracked but once the level was correct the water stopped and the boiler was working well. I think.
So here is the question. How does the water come out of the boiler if I overfill it? Is there some kind of valve the will open for water but not steam? Or is my boiler on its way out?
This is a Bryant Gas fired boiler. I believe the boiler is pre WII from Germany
I live in Providence RI I anybody know someone who loves steam heat and know this stuff inside and out please contact me.
Dan