Not many people left with single glazing unless they've been trapped by historic building rules. "Outdoor plumbing" is not a thing.

The pump is a drop in replacement unless you have 8mm "microbore" piping, at which point the lower temperature times restricted flow rate becomes a problem in terms of getting enough heat through.

My parents' house in Bath is not "trapped by historic building rules" but there is no way in hell they are ever going to replace 3-4 stories of single pane glass double hungs ...

and that house still has the sewage stacks on the outside of the house, as do almost all homes in Bath and environs.

Not sure about the UK. I've seen a lot of outdoor plumbing in Ireland. I lived in a place that had that. They were literally running on the outside. Our maintenance guy said they did that to make maintenance easier, but it also makes wear & tear a lot easier obiously (not to mention frost). And chipboard floors that would crack with heavy furniture. It was terrible quality. These houses were built in the mid 80s.

And a dirty tank of water in the attic to act as a "in-house water tower" because only one tap may be connected directly to the mains. Really archaic.

By 'outdoor plumbing' they probably mean pipes running up the outside of buildings (not, like, outhouses). This is somewhat common for waste pipes.