I've seen a few possible solutions to this problem but need some more help! The radiator in my bathroom has been cold for over a year and I've finally got of my backside to do something about it. The house has an electric combi-boiler and several radiators upstairs and downstairs. The bathroom radiator is upstairs and both pipes leading to it are cold when the heating is switched on. Both sides of the radiator are attached to the plumbing with what I believe is a lock-shield valve (white removable plastic cap with a bar underneath that can be turned using pliers). I have undone the nut that is at the top of the valve and noticed a lot of metallic gunk underneath and when I start turning the valve with the nut undone water starts flowing but it's always cold.