Check the Shutoff Valves Under Your Sinks for Green Crust

The Problem

The angle stop is the little valve on the wall behind a fixture — hot and cold under every sink, one behind each toilet, usually a pair behind the washing machine. It's the thing you reach for when a supply line starts dripping at midnight.

Nobody ever operates them. A valve can sit in one position for twenty years while the internal washers harden and the stem seizes, and the first time anyone finds out is the day something else has already gone wrong. The failure this creator has seen at its worst: the valve came apart in the homeowner's hand, and water ran for the two or three minutes it took to find the main shutoff — long enough to do serious damage to the property.

What to Look For

Get a light and look closely at the valve body and the joints either side of it.

  1. Whitish-green crust on or around the brass is corrosion. That's the main tell, and it means the valve has been weeping slowly for a while.
  2. A stem that won't turn, or turns and doesn't stop the flow, means the internals are already gone.
  3. Any moisture, staining, or mineral deposit on the cabinet floor beneath the valve points at the same thing.

The replacement interval worth planning around is 10 to 15 years. A decent valve is a $20 to $30 part, which is the whole argument for doing it on a schedule rather than in an emergency — the part is trivial next to the cost of a flooded floor.

Pro tip: If you're buying a house, this is a job for the window between closing and moving in. The valves are accessible while the cabinets are empty, nothing is at risk if a line has to stay off for an afternoon, and you start ownership knowing every fixture in the place can actually be isolated.
Safety note: Before you touch any of this, find your main shutoff and confirm you can operate it — it's subject to exactly the same seizing as the angle stops, and it's the valve you'll want if one of them lets go while you're testing it. Replacing an angle stop means working on a live supply line; if the valve is corroded enough that you're worried about it, that's an argument for having a plumber do the swap, not for exercising it to see what happens.

Electrical, plumbing, and structural work may be regulated where you live — check local code before you start, and note that a permit may be required. More in our disclaimer.

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