Hi ive just installed x4 new radiators for an extension and teed into the existing return and flow. I think ive got severve air in the system. x1 is hot and bleeds fine, x2 are hot but i can remove the bleed nipple and no water comes out and the another is cold, water bleeds out(cold) but the pipes are getting hot towards it. Ive tried bleeding at the pump as well. When i remove the screw water just drips out. Should it come out with force? can i leave the screw out as i can hear air coming out now and again untill water really starts coming out? The boiler is a back boiler not a combi and all the existing radiatorts worked fine before, thanks for any help cheers Rick