No heat from new radiator?

I have just removed a radiator from the down stairs living room wall and blanked off the pipe work.
I have fitted a new radiator to the opposite wall, but because the floor is concrete i have taken the supply and return from an upstairs bedroom radiator approx 4 meters each flow and return. The radiator will not get hot.
I have turned all upstairs rads off, still no good.
I have checked the new rad for blockage ok, I have checked both of the new valves for blockage ok.
I am no expert but I thought it should have worked.

I f you could be of any assistance in what to try next it would be appreciated.
Thank you

Joe
October 2009