advice re potterton netaheat 16-22?

is it only one rad or more downstairs ?
the valve maybe full of crud or faulty. is it fully open ?
the return pipe going back up th wall maybe air locked.

check all the valves on the rad are open.
turn upstairs rads off and the full flow off water should push the airlock out. if this works the system rads are not balanced properly

hi-spec plumbing & heating (essex)
September 2008