Hi Tracy
If it has two valves (normal control valve and a lockshield valve) make sure they are wide open.
Now close the valves on the other radiators to make the pump push the water to the cold radiator.
It may be that other radiators are robbing it of some circulation pressure or there is a bullet of air preventing the water from flowing. This usually happens when the radiatior is fed from drop feeds from above. Either way if the central heating water is hot you should be able to feel the water beginning to enter the radiator within a few minutes. It may even dislodge a bullet of air into the radiator-if so -bleed it.
If it works either turn up the speed of the pump or throttle down the lockshield valves on the other radiators to stop them robbing the pressure until you get them all balanced. Remember smaller radiators need much less flow than the big ones-so start with them first.
Geoff - hiding out somewhere in Wales, December 2010
