Is there a friendly plumber/heating engineer looking in? One of my gas central heating radiators has suddenly stopped heating up. The radiators are thermostatically controlled and I have tried opening it to maximum but no joy. This has never happened before and I am stumped. Any ideas would be appreciated. This just happens to be in the coldest room in the house!
I had the same Issue, shut off all other rads & direct all the hot water to the cold rad, I take it you have bled it? have you checked if the valve is working? check the IN/ OUT pipes below the rad, are they hot? another cause is a blocked rad this involves shutting off the rad taking it off the wall & flushing it, has that been done?
If it's definitely the whole of the radiator which isn't heating up (rather than just part of it) it's more likely to be a dodgy TRV (thermostatic radiator valve) than a need for bleeding.