Radiator only heats up when all others are turned off

Hi,

I have a radiator upstairs which wont heat up unless I first close all other radiators off, even then it takes a while for it to heat up, I then turn back on all other radiators. However once I turn the heating off then the next time I turn it on again the same radiator wont heat up, does anybody know what I need to do to fix this? I really dont want to have to close all other radiators first then turn them back on each time I turn the heating on.

Thanks