Help! Someone (who does know what they're doing) took my new towel rad off for me to decorate. My son and I have put it back on (thought we'd try, although the guy who took it off said to call him and he'd replace it). I fitted it correctly, bled it, did the pressure on the combi and it was lovely and hot. Now, all the other rads are on, but the towel rad is stone cold. What have I done wrong???!!!