On most designs it can, which is the reason the product line exists. The valve is accessible through the face plate, so it can be isolated upstream and changed in place.

That depends on the box having been installed with the valve properly aligned behind the aperture, which is why installation position matters so much on these products.

Where the original was fitted badly, or a non-standard valve was used, the repair can genuinely require opening the wall, which is a much larger job in a tiled room.

By the box platform it belongs to rather than by appearance. Manufacturers make valves to fit their own housings, and the body dimensions and mounting differ between platforms even where the visible handle looks identical.

The box usually carries a model marking inside the housing or on the plate, and that is the number to work from.

Photographing the valve in place, with the plate off, is more reliable than describing it, since several platforms share a family resemblance and take entirely different cartridges.

The vertical run of supply tube inside the wall that carries water from the branch up to the box. It is not the same thing as the flexible tail from the box to the fixture.

Risers are sold in defined lengths and materials to suit the box and the wall build-up, and choosing one that is too short is a common cause of a strained joint at the top.

On a replacement, the existing riser is often sound and only the valve needs changing, so it is worth establishing which part has actually failed.

Physically, sometimes; practically, they behave differently and it is worth choosing deliberately. A quarter-turn ball valve either seals or does not, and it is quick to operate in an emergency.

A multi-turn valve closes gradually, which some installers prefer for throttling, but it relies on a washer that perishes and can weep for a long time before anyone notices.

For a valve that will sit untouched in a wall for years and then be needed urgently, quarter-turn is generally the better specification.

Rarely from use, because most are operated a handful of times in their life. They fail from sitting still — seals hardening, and mineral deposits binding the mechanism.

That produces the classic failure: a valve that will not turn when it is finally needed, or one that turns and then weeps because the seal has taken a set.

Operating each isolation valve occasionally as part of maintenance is the cheapest preventive measure, and it is very seldom done.

Not necessarily, but it is usually sensible. A braided flexible line has a service life and is cheap relative to the labour of getting to it.

If the line is old enough that the valve has failed, it is old enough to be worth changing while everything is apart and the water is off.

Flexible lines are also one of the more common causes of escape-of-water claims, so replacing a tired one is worth more than its cost.

Matched to the box platform on the inlet side and to the fixture standard on the outlet, which is why a valve is described by both.

Mixing a valve intended for one thread with an adapter to reach another is possible but adds a joint inside a wall cavity, which is exactly where a joint should not be.

Where the correct part for a platform is genuinely unavailable, replacing the whole box is often the sounder repair than adapting a valve to fit.