replaced main vents, boiler flooded

mjbr24

i just replaced 1 of 2 hoffman #4 main vents with Jacobus #1. The boiler fired up before i changed the second one because it's buried in the ceiling. i let it run and the boiler completely flooded up into the main lines. this has never happened before. (I am ordering Dan's book, BTW). I noticed on Hoffman's website that #4 vents are vacuum and #4A non-vacuum. I have gas heat, so I thought the #4s were always wrong and I needed a non-vacuum vent (Jacobus #1). Was the flooding because I only changed 1 vent and had a "bad" one still on the other main? should I be using Jacobus #1s?

Steamhead

Something else went wrong

Two possibilities are a leaking water feeder, or a blocked return line. The vents did not cause this.

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mjbr24

i just fired the boiler up again with the new vent after draining the water down. the water remained at the proper level and the boiler provided heat to all radiators before cycling off. if i had a blocked line, is it possible that it is clear now? thanks for the info. it's people like you who make this site great.