I recently had the plumber round because I had to have a new thermostatic valve on one radiator, another radiator wasn't working and the three way valve was faulty. It turned out the pump had to be replaced as well, but in getting the problem found all rads had to be turned off. I turned off the one side of the ancient towel rail the plumber looked at the other side but abandoned the idea of turning it as he thought it might break. Now the radiators are working well, but the towel rail hasn't heated up after I turned on the side I had turned off. I've tried bleeding it and each time a little bubbly water comes out before it runs easily, but it still isn't heating. I think it is connected to the hot water circuit.