Single zone baseboard heat (cast iron) but one floor is not getting hot..

Hello all. I have a split level home with 4 floors. The top 2 floor baseboard get really hot but the bottom level does not. The boiler is in the basement which is finished but it is hot for the heat thrown off the boiler. Yesterday I did some research one end of the baseboard has a nozzle so I screwed a hose on it and let out a lot of water and it got hot on that side of the cast iron baseboard but not the other. There was a bleed valve on the other end so I bled it until the water was hot and then the whole baseboard got really hot but did not stay hot. There is a valve under the bleeder that I turned but did not hear water going through so I think it may be broken.. Anything else I can try before I call someone to replace the valve.. This room that the baseboard is in is against the wall next to the garage so it was freezing on that level the last couple day here in nj..