Hi can anyone help save my sanity?? I recently drained down my central heating system as i had a leaking valve and while it was drained down decided to replace a downstairs rad to a double. When i refilled the system i added an inhibitor to the new rad, bled all the rads and switched on. All downstairs worked a treat but 3 upstairs rads stayed cold. These are original rads so probably about 30years old. I tried bleeding them and the next day one went hot but two still refuse to play. I have tried to bleed them (taking out about 8 litres of water out of each one so there is no air in them)I have felt the flow and return pipes on the combi boiler and both get red hot so water is obviously going round the system. Any help greatly appreciated.