Cold radiator

[JT]

I have a radiator on the gravity feed part of my central heating system which has stopped heating up. There have been no alterations or any work carried out on the system.

I have drained the radiator and then slowly filled it from each of the valves in turn, just to ensure that there was no blockage, and it filled with no problems. There is no air coming out out when I bleed the radiator only water. The pipes up to the valves are hot or at least one is and if I bleed the radiator some heat comes in as hot water replaces what has been bled out.

The gravity system feeds two radiators and the hot water cylinder, the radiator which does not work is closest to the cylinder. The pumped heating can be on or off and does not affect the gravity system.

 

[MANDATE]

I know you have used both valves for filling the radiator but there could be a partial blockage below one of the valves which would allow you to fill the radiator slowly but could prevent water circulating through it fast enough. On the other hand the blockage could be in the radiator.
I would suggest the rad is removed and washed out and all sludge removed. With the rad removed you could open each valve in turn to run some water off and prove there is no restriction. It is better doing this with a short hose pipe fitted to the valve.If its a standard valve I think you'll need a 1/2 in tap connctor to secure the hose to.