Bart C wrote:
Would there be any problems installing a downstairs radiator fed with pipes
from the floor above?

It's run from a vented back boiler with CH pump.

Thanks, Bart

No, it's quite common.

You just need to be sure that the pipework can take the extra flow -
chances are that unless you are adding a huge rad to an already well
loaded circuit that all will be fine. Personally I would add a drain
point on this rad to help with future servicing - otherwise there will
be a lot of water to catch if you ever need to remove the radiator.