I would be very grateful if anyone can help.I have an open vented system. I drained down my central heating system to fit a new radiator in my utility room, the new radiator is the first one coming off the boiler, i teed off the 22mm flow and return about 1 metre from the boiler. i fitted the radiator and refilled the system. The radiator and all the rest down stairs work fine, but the ones up stairs stay completely cold, i've tried venting all the radiators but it made no differents, The only thing i can think of is when i drain the system down i did not open the vents on any of the radiators, do you think i may have an air lock in the pipes ? don't want to drain it down again if can help it, as put some inhibitor in,