Howw can I fix my FERROLI DOMINA 80 E, radiators only partially warm ?

I have had the above above model in my house for some time, and have not at all been satisfied with the heating output, the radiators, are only partially warm, hot at top and cooler at the bottom, however if the heating dial is left on, then some heat does eventually reach the bottom. I have had the so called 'Power Flush' a couple of years ago, hot water is ok, allbeit slow from the taps, again the dials have always had to be turned up, I am just wondering, would the pump have to be turned up to allow a faster flow rate around the system ? I haven't a clue, but at the edn of the day, the 'rads' aren't heating the rooms !! HEEELP !!