Thanks for the recommendations and tips. Have someone local coming tomorrow now, will let you know how we get on (would give out his name but I know he's retiring shortly).
It's not the furthest away, but we have a feeling this one might have been turned off for quite a few years as it's next to a desk and DH started working from home 2008.
It's been off the wall and been flushed with fresh water. I saw some black sludge come out initially but only a little bit.
We've had a water softener for quite a few years now so we don't suffer from scale.
