Hello Good afternoon, I hope I can give you some idea as to your problem.
You say that you have bled the radiators of air. As this is the last radiator of the circuit it may be that the water pressure is not high enough in the system. Have alook at the dial on the boiler the pressure should read 1 to 1.5 bar. if this is low add water from the tap under the boiler until the pressure is correct.
The other reason may be the radiators are not in balance, if you try half shutting some of the others this may help to increase flow to the latter ones. Try this and come back to me if this does not help.
I am off to work now but I will look and see if there is a reply on my return.