radiators going cold

[murphs1]

Hi there can anyone help. I recently had an extension added to the house and we have added 4 radiators to the system. The upstairs ones that are furthest from the boiler barely warm up. If I shut down all the other 13 rads most of which are doubles I can get the furthest really very hot. As I open the others by opening the flow valve wide and restricting the return valve the new rads gradually go down to luke warm. Someone suggested that I add an additional pump to the system upstairs and wire it so it goes on and off with the existing pump which is by the boiler. Has anyone any experience of this type of arrangement. Is it a good idea. I would really appreciate any advice.
Thanks

Pete

 

[steve32]

is boiler under sized
the most common problem in adding extra rads to a system will be under sized pipework
have you upgraded existing pipework to allow for new rads
are the new rads connected into 22 or 15 pipes
what size is the pump