As per the title. I've fitted a heated towel rail (duel fuel) in place
of the bathroom radiator. It's quite a tall one, much higher than the
previous rad, but it filled up with no problems. I've bled all of the
rads, there is still a slight gurgling from the pump but nothing
excessive. I've got no heat in any of the downstairs ones - not even
slightly warm. All of the upstairs ones are really hot.

The water was relatively clean so I don't think anything's sludged up.

Have I upset the balance somehow? I've tried turning the towel rail off
completely but that makes no difference.

Or have I got an airlock? I've drained/refilled the system before and
didn't have any airlock problems then.

TIA
--
/Simon