Why would my GCH radiator have stopped working Every other radiator is fine and I have also bled the radiator but it won't heat up?

If GCH operating on steam- check trap for particulate plugging or failure. If on hot water, check flow of other radiation and possibly reduce flow to units that are operating "hotter" than others. Is freezing of the pipes to the non-op unit possible? (Don't know where you live, temperature wise). Pump operation could be checked to verify performance relative to the pump "curve" with an ammeter and infrared thermometer (using GPM vs: BTUH formula). Also, if piping is old, and not treated with chemicals to prevent corrosion, the piping could be restricting the flow to this radiator. (Also applies to steam) lc