Plumbing and maintenance
Isolation valves: small fittings that save whole days
The short answer
Service valves on each appliance and outlet let one tap be worked on without draining the house. Their absence is why small jobs become big ones.
Your questions answered
Can isolators be added later?
Yes, usually during any other plumbing visit while the water is already off.
Do they fail?
Occasionally the small spindle seizes; they are cheap to replace when accessible.
The practical points
Point 1
Fitting isolators at basins, WCs and appliances turns a future washer change into a ten-minute job.
Point 2
Valves should be accessible after the room is finished; burying them behind sealed tile defeats the purpose.
Not ready to book, just weighing it up?
That is fine, questions at the thinking stage are the cheapest ones to ask, and they usually save a change of mind later.