Replace a Corroded Angle Stop Under the Sink: 7 Steps

TL;DR: A corroded angle stop (the shutoff valve under a sink) should be replaced once it's leaking, won't turn, or shows green/white crust on the fitting. Shut off the home's main water valve, cut or unscrew the old stop, and sweat or thread on a new quarter-turn valve for about $8 to $15 in parts. Budget 30 to 60 minutes if the supply line is copper and cooperative, longer if the valve is fused to old pipe.

_Last reviewed: July 2026 · 6 min read_

The little valve under your sink is easy to ignore until the day it won't shut off, or worse, starts dripping onto the cabinet floor. If you've noticed green crust, a stiff handle, or a slow weep at the nut, you're looking at a corroded angle stop that needs to come out before it fails on its own schedule.

Okoniq Property Hub keeps a maintenance log for every unit, so a leaky angle stop you fixed this spring shows up automatically when it's time to check the rest of the fixtures next year.

Why do angle stops corrode in the first place?

Angle stops corrode because they sit at a joint where two metals, minerals in the water, and constant humidity meet for years without attention. Most homes built before the 1990s have chrome-plated brass valves, and the plating wears through at the packing nut and the compression fitting, exposing bare metal to drips and condensation.

Hard water speeds this up. If your area runs above 7 grains per gallon of hardness, mineral deposits build a crust around the valve stem that locks it in place, so even a valve that isn't leaking may not turn when you finally need it to. That's the real danger: a stop that looks fine but has seized shut fails you exactly when a supply line bursts and you need to shut water off fast.

How do you know it's time to replace instead of repair?

Replace the valve if you see any active dripping, a chalky ring at the base, or resistance when turning the handle more than a quarter turn. A little surface tarnish on the chrome is cosmetic and not a reason to act, but moisture that never fully dries around the nut means the seal inside is already compromised.

Try turning the valve clockwise to fully closed once a year as a test. If it groans, cracks, or won't budge past a certain point, don't force it. A cheap 20-year-old angle stop under stress from someone leaning on a wrench is how a routine check turns into a flooded cabinet. If the valve is frozen and you can't isolate it, that's the point to snake it yourself or call a plumber-style judgment call: try once carefully, then stop and call a pro if it won't cooperate.

What tools and steps do you need to actually replace it?

You need to shut off the home's main water supply first, since the angle stop itself is what controls water to that one fixture. Here's the sequence:

1. Locate the main shutoff (usually near the water meter or where the line enters the house) and close it fully.
2. Open the faucet above the sink to relieve pressure and drain the line.
3. Place a small bucket or towel under the valve, then unscrew the compression nut connecting the supply line to the valve using two adjustable wrenches (one to hold the valve body steady).
4. Remove the old valve from the copper stub-out. If it's soldered on, you'll need a tubing cutter to remove the old fitting cleanly.
5. Slide a new compression nut and ferrule onto the stub-out, then thread on the new quarter-turn valve.
6. Tighten the nut hand-tight, then a quarter turn more with a wrench. Don't overtighten; brass ferrules crush and seal without much force.
7. Reconnect the supply line, turn the main water back on slowly, and check every joint for drips over the next 10 minutes.

Total cost for a basic quarter-turn compression valve runs $6 to $15 at most hardware stores. If the stub-out itself is corroded, pitted, or the wrong length, that's closer to a job for a plumber, especially if it turns out to be cast iron or older galvanized supply piping rather than copper.

Compression valve or quarter-turn ball valve, which should you install?

Quarter-turn ball valves are the better long-term choice for most kitchens and bathrooms. They shut off with a 90-degree twist instead of multiple turns, and the ball-and-seal design resists mineral buildup better than the old multi-turn washer style.

| | Multi-turn (washer) valve | Quarter-turn (ball) valve | |---|---|---| | Shutoff speed | Several full turns | One quarter turn | | Mineral resistance | Lower, washer wears | Higher, smooth ball seal | | Cost | $4-$8 | $8-$15 | | Lifespan | 8-12 years | 15-20+ years |

The few extra dollars for a quarter-turn valve pay off the first time you need to shut water off in a hurry, and they're what most inspectors and plumbers install by default now.

What if the main shutoff won't turn either?

If the home's main valve is also stiff or won't fully close, treat that as a higher priority than the angle stop itself. A whole-house shutoff that fails during an emergency, a burst line, a hose bib freeze, means you can't stop water anywhere in the house. Exercise the main valve twice a year, and if it's original to a house built before 2000, plan to have it replaced by a plumber even if it isn't leaking yet. The same seasonal-check habit applies if you're closing up a home for months at a time; a working main shutoff is what protects the place while no one's watching it.

FAQ

How long does an angle stop valve last before it needs replacing?

Most chrome-plated brass angle stops last 15 to 20 years under normal water conditions, but hard water or a house with galvanized supply lines can cut that to 8 to 10 years.

Can I replace an angle stop without turning off the main water valve?

No. The angle stop only controls water to that one fixture, so you must shut off the home's main supply before removing it, or you'll be working against full house pressure.

Is a dripping angle stop always a sign it needs replacing?

Usually yes if the drip comes from the valve body or packing nut itself, but if the drip is only at the compression fitting, sometimes tightening the nut a quarter turn solves it without a full replacement.

What causes the white or green crust on an angle stop?

That crust is mineral deposit (often calcium or copper corrosion) building up where moisture has been sitting on the metal for a long time, and it usually means there's been a slow, unnoticed leak at that joint.

Do I need a plumber for this repair?

Not for a standard copper supply line with a compression fitting; most owner-operators can do this in under an hour with basic wrenches. Call a plumber if the stub-out is corroded through, soldered with no room to work, or if the main shutoff also won't close reliably.

This is educational information, not plumbing or legal advice. Call a licensed plumber if a valve won't close, if you're unsure about shutting off your main water supply, or if you find signs of water damage beyond the immediate fitting.