I've just had the plumber round to fit a new pump. The port valve was also changed. Now the ancient towel rail is cold, having been reliably hot before. I can feel the pipes are hot near the floor. I have unscrewed the chrome covers at the top and tried bleeding it. I'm getting some bubbles then water escapes. Leaving it for a bit then the same thing. Should the big tap near the bottom be screwed in or out? I know the plumber was fiddling with it, but don't know if he left it as he found it. I've also bled the two radiators on the floor above. The ones on the same floor seem fine. Any help appreciated.