It's the kind of thing I would do now. It will be relatively easy to pull a new cable through, as you have the old one to use as a drawcord.

Might as well do it now while you're crawling about anyway.

In reply to a post by shtu:

It will be relatively easy to pull a new cable through, as you have the old one to use as a drawcord.

I think that'd depend on how many and the angle of any bends in the cable as well as diameter of any conduit and possible snagging with the other cables running through the same conduit.

It's a fairly straight run - 7 metres down a wall and then under the floor - but that is through various noggins and the underfloor heating pipes are there too! It sounds easy - but I know it will be a pain - the break is possibly halfway down the wall at a point where I have access ...

Can you get junction boxes rated at Gb? Any I've seen before weren't rated that high, though I've not often looked...

Apparently, yes. They are the ones with Krone terminals capable of taking two wires rather than two strips of terminals and a small PCB. If I do that and it fails, I will still have 100Mb.