Quick answer
Isolation valves — usually the small 15mm chrome ones under basins — seize precisely because they are never operated. The one you need in an emergency is the one that has sat untouched for a decade. Forcing a seized valve commonly strips or snaps the spindle, and then you cannot isolate at all. A plumber replaces them properly with the supply off.
Common causes
- Never operated, so the mechanism has seized in place
- Mineral and scale build-up around the spindle
- Plastic spindle stripped by previous forcing
- Corrosion between the valve body and the internals
- Cheap valve with a marginal mechanism from new
- Debris from supply work jamming the ball or gate
What you can do now
- 1Do not force it — a stripped spindle leaves you unable to isolate at all
- 2Exercise every isolation valve in the house once or twice a year so they stay free
- 3Locate your main stop-cock now, so a stuck local valve is not a crisis
- 4Note which valves are stuck so they can all be replaced in one visit
- 5Clean visible scale around the spindle before trying gently again
When to call a professional
Have the valve replaced while the supply is off, and ask for any other seized valves to be done in the same visit — the cost is mostly in draining down, not in the valves themselves. It is worth doing proactively before a renovation or before any appliance installation, because that is exactly when you discover the isolation valve does not work.
Typical cost in Johannesburg
R350–R650 each
Indicative ranges only. We provide written, itemised quotes before any work.
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