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I have been advised that I need a main steam vent on my gas boiler. The main runs approximately 60" from boiler to an elbow that runs approx 10" and branches up to first floor. Would the vent be installed on the pipe before the elbow? Note: The technician that came explained he doesn't do this type of work but said the reason my first floor radiator valve is shooting hot water (new valve/radiator properly pitched) is because I have no main steam vent.