Just found this post, not sure if the gasman is out or not! But have tried your suggestion and still have a cold section on the bottom of my rad. Had a ladrge kitchen extension a few months ago, added 3 new radiators two small ones, and one huge one 1.2m long and about 400mm high. All the radiators in teh house are so hot you cannot touch them, the large one is warm on the top and luke warm on the bottom, have tried bleeding, draining, and of course your suggestion, stilll the same? Any ideas what to do next? This rad is the main rad for the extension, 11,500btus