Cut back as far as possible (if you haven't already done so) then either cap both ends or fill both ends with squirty foam as far as possible (no point in doing both) Make sure that the outside of the pipe is airtight to its surroundings.

Posted By: djhIt's difficult to say much without seeing the actual thing, But definitely try hard to cut away as much of the inside pipework as possible. I don't suppose you can get a good enough grip to twist the thru-wall section loose and pull it out? Don't cap with copper ends, because that just increases the heat loss surface. Maybe use some hard plastic or wooden plugs in the ends. Squirty foam is no use at the ends because creatures will nest in it.

It's also difficult to see the actual thing!

Some more details. The pipe is 22mm copper with soldered elbows. It ran horizontally west into the boxing. Now cut off flush with the boxing. Looking and poking a stick into the hole suggests that the first elbow is 120mm in. It then goes 1100mm vertically down, presumably to a second elbow. Then 300mm horizontally south through the cavity wall (built in 1996 - blockwork; insulation; air gap; brick?). Exits the house 250mm above ground level with another elbow to deflect it downwards.

Might be able to find out more when the electricians opens up the boxing for some wiring changes. They also have a really handy Ferret (https://ferrettools.com) for looking into hard to reach places.

Should be possible to cut away some more of the inside pipework. However, the remaining 'L' shaped section will make twisting it difficult ...

On the outside, the elbow can easily be removed. My first thought was to perhaps use something like a Dremel to trim back the pipe to behind the surface of the brickwork. An Internet search for "internal pipe cutter" suggests that they exist but appear far from common and may not be suitable for 22mm copper. Maybe a tool like that used for fitting Condensate Pro (https://condensatepro.co.uk) could be used to remove a plug of brickwork? Unfortunately for me, I have a live condensate pipe which is probably too close to the redundant pipe for that approach.

Looking on DIYnot (https://www.diynot.com) the expanding foam approach is common. If sprayed from the inside there seems a good chance it would go right through the pipe. I have no experience with the stuff myself and am anxious about creating a Sorcerer's Apprentice situation with the street filling with unstoppable foam.

Posted By: john.connettMight be able to find out more when the electricians opens up the boxing for some wiring changes

I was going to suggest drilling a hole in the boxing inline with the exit pipe, but if the electricians are opening it anyway ... excellent :)

Don't be in too much of a hurry to take the elbows off as they'll provide good leverage for twisting the pipe if desired. Leave the elbows until near the end. A dremel to cut back to the brickwork sounds good if you have to leave the pipe in place.