Cold radiator?

Have one cold radiator upstairs. Was fine until turned off last winter. Had British Gas engineer to do assessment wanted 650 pounds to power flush, as well as 31.50 per month for one year. Done the job ourselves today. Alas radiator still cold after all that trouble. The valves have been checked and have tried turning all other radiators off etc., We are stuck with this, anyone have any more suggestions?
Combi boiler, 9 radiators.
Thanks