Thanks Lumat,
I have already tried to balance system, all rads have been shut off (except one) the last three have been left fully on (all three in the same room in a seperate building) and they have become very hot. I then moved down through the system proportinally opening the return valves, the closest being almost closed. I lost the heat from the furthest three rads with the flow not wanting to take that route. I have experimented with return valve positions but to no avail. My thoughts, if i can't change the pump within the boiler and i can't easily increase the pipework diameter to 22mm then a second equally sized pump running in the same direction as the boiler pump would assist the flow to the last three rads. Thanks for your thoughts so far dave
