radiator not heating

jrh

in a recent steam boiler replacement i was setting up the new lgb 5 at half a pound cut in with one pound differential. the old boiler ran between 3 and 4 pounds. probably trying to overcome bad traps. i sized this boiler per square feet of existing radiation with a pickup factor of 20%. i reinsulated all lines. corrected sagging pipes in main and most condensate return lines. 3 inch main. some radiators heating only half way and one not heating at all. i am currently replacing traps. but wonder why no heat in one radiator right over mechanical room. condensate return is slightly backpitched. before i suggest correcting i need to know if the new correct low pressure is not overcoming the trapped condensate. also should cast iron baseboard be pitched one inch for twenty feet when its a two pipe system. some are back pitched. this house was converted from radiators to c.i. baseboard 40 years ago.

any input appreciated.

bigugh_4

IF

The backpitch is enough to block off the pipe with condensate It'll sure will stop the heat. If is is only slight and the steam has to pass over it to get to a vent, it could bang like heck. SO proper grade on all pipes is essential. Once again, Sand cast, cast iron, heating elements can have sand blocking their passage ways. This can build up over time in a place convienent for it to happen. The cold BB may have to be removed and cleared out. Seen it more than once!