The semi we are in HAD 7 radiators, the largest being the Living room, I just replaced the Single with a double making 8, the system was checked & no Air Locks except this new living room one, I bled this new rad for about 20mins to make sure the system was clear of air, all ok, today the new rad has lowered it's heat output, checked back to the "Unmarked of any info pump" then up to the 4 out lets in the line, 3 plastic pipes Hot except the plastic pipe going from the same 4 outlets to the new rad, does anyone have an Idea why this new rad does not keep the heat only warm not hot, the valves are open. Puzzeled!!!!