Spiting radiater out of vent

peter petruzzi_2

I have a recessed radiater in the 2nd floor apt. that spits 1gal of water out in 24hrs. from the air vent.Taco will stay closed,noheat,no water.Vari vent allows water to spit out and radiater will heat up.Flushed boiler fom skimmer 3 times.new boiler.Just bought house dont know what old boiler did.Hartford loopwas done right.No valve on radiater.Put squik in boiler.Returns tied in below boiler water line.Mains pitched away from boiler.Took union apart blew in riser with ventoff.Water shot out.Radiaterblocked?Was told not possible!Pressure set1andhalf lbs.Radiater is in middleof house.Nobody has a clue.Riser goes up in wall,outin floor over 3feet into wall up to radiater.NO VALVE,so not a droppedwasher.HELP!!!!