Cold fin radiator on new oil burner installation

[freepaul]

A plummer replaced my old oil boiler with a new Crown oil bolier last week. I bled the fin radiators on saturday while runing the furnace and circulator for 45 minutes. There was air in the radiators on this mono flow heating system. I got all the air out from all radiators. I noticed the last radiator on the heat line never got hot even when all the air was bled out. I repeated the same procedure today with the same results. It seems that the pipe leading to the last fin radiator is hot but the return pipe is cold. The boiler temperature on the aquastat was 175-180 degrees with the pressure about 35 to 40 lbs pressure but the new 30 lb presure relief valve never blew off. What is causing the last radiator on line NOT to become hot? Should I be removing some water from the large metal expansion tank?

[johnjh2o1]

Try bleeding the system with the circulator off. This will allow the air to go the high point of the radiators where the vents are. Also your boiler pressure should be between 12 - 15 lbs. It may be a faulty gauge as the relief valve should have opened at 30 PSI.

John

[freepaul]

Thanks John for your reply. After looking at the gauges again with a flashlight, the pressure gauge is reading 18 lbs pressure. I did try bleeding without circulator and heat on and there was no air trapped in the radiators. After looking at this cold specific last radiator 1/2 inch RETURN pipe, I noticed that the elbow leading up to the radiator is about 1 inch lower than the top of the tee fitting on the main 1 1/2 inch black pipe. The reason for this not being above or level with the tee of main pipe is that the original plummer had to cross under the main beam to reach the final radiator return pipe in the heating system. I do not recall having this specific cold last radiator problem for the last 25 years when the original oversized boiler was operating. Would this cause that last radiator to be cold?