How to Replace Water Shutoff Valves Under the Sink

Water shutoff valves under your sink are the first line of defense when a leak happens. They're also the most ignored plumbing fixture in most homes—until the moment you need one and it won't turn, or it leaks when you do. Replacing them is straightforward work that requires no special skills, just patience and two wrenches. A stuck or leaking shutoff valve means you're one burst supply line away from calling an emergency plumber at midnight. The good news is that new valves are cheap, the work is mechanical, and once it's done, you've actually solved a real problem instead of just living with the worry.

1. Shut Off Water First. Locate your main shutoff valve, usually near the water meter or where the supply line enters your house. Turn the handle clockwise until it stops. If you can't find it or it won't turn, call your water utility for help—they can shut it from the street. Wait 30 seconds, then open a faucet upstairs to bleed pressure from the lines.
2. Clear Your Workspace. Slide the towel under the sink to catch drips. Open both cabinet doors wide so you have room to work and can see what you're doing. If there's a garbage disposal or P-trap in the way, you may need to move it slightly or work around it. Clear out any boxes, cleaning supplies, or junk first.
3. Find Both Valves. Look at the supply lines coming into the base of your faucet. You'll see two copper or plastic lines (hot and cold), usually with small oval handles or knobs on them near the wall or the sink base. These are your shutoff valves. Even though you've shut off the main, these isolation valves let you work on just the sink without affecting the rest of the house. If you don't see them, you may have older plumbing without isolation valves—in that case, you're replacing the stubs themselves.
4. Disconnect Supply Lines. Use an adjustable wrench on the nut where the supply line connects to the shutoff valve. Hold the valve body steady with another wrench so it doesn't spin. Turn the nut counterclockwise until it loosens, then finish unscrewing it by hand. Water may still drip—let it run into your towel. Do this for both hot and cold lines.
5. Unthread Old Valve. The shutoff valve is threaded onto a short piece of copper pipe sticking out of the wall or floor—this is called the stub. Use two wrenches: one holding the stub steady (or use a pipe wrench gripped tight on the stub) and the other turning the valve counterclockwise. The valve will come off in your hand. If it's stuck, apply penetrating oil and wait 10 minutes, then try again with steady pressure—don't force it.
6. Clean All Threads. Use a wire brush or old cloth to scrub the threads on the stub until they're clean and free of corrosion. If there's old thread sealant or tape, pick it off with your fingernail or a plastic brush. The cleaner the threads, the better the new valve will seal. Wipe the stub dry with a cloth.
7. Seal Threads With Tape. Wrap plumber's thread tape (also called PTFE or Teflon tape) around the male threads of the stub, going clockwise three times around. Press it down as you go so it sticks and doesn't bunch up. This prevents leaks at the connection. For extra security on an old or slightly damaged stub, apply a thin coat of pipe thread sealant compound (a thick, white paste) over the tape.
8. Hand-Thread New Valve. Thread the new shutoff valve onto the stub slowly, turning it clockwise by hand until you feel it catch the threads. Don't use wrenches yet—hand-tightening lets you feel if the threads are aligned. If it starts to bind or feels wrong, unscrew it, check the threads, and try again. Getting the first few turns by hand prevents cross-threading, which ruins the fitting.
9. Secure With Two Wrenches. Once the valve is hand-tight, use one wrench on the valve body and one on the stub itself, turning the valve clockwise until snug. Don't over-tighten—you're looking for a firm fit, not a death grip. Quarter-turn to half-turn more after you feel resistance is plenty. Over-tightening can crack the valve or strip the threads.
10. Reattach Supply Lines. Thread the nut of the supply line onto the outlet of the new valve by hand first, then tighten it with your adjustable wrench while holding the valve body steady with another wrench. Make it snug but not bone-tight. The connection should feel solid with a quarter-turn more after you feel resistance.
11. Restore Water Carefully. Go to your main shutoff and turn the handle counterclockwise slowly—it should take 10 to 15 seconds to open fully. This gradual fill prevents air locks and pressure spikes that can pop fittings. Come back to the sink and look for any drips around the valve connections. Wait two minutes to ensure nothing is leaking.
12. Verify Valve Function. Once water is running normally, carefully turn the handle on your new shutoff valve clockwise—it should stop the water flow to the sink within one or two turns. If it doesn't, the valve may not have seated properly; close it and retighten the connection on the stub. Then turn it back on and try again. The valve should feel smooth and positive, not loose or grinding.
13. Monitor For Leaks. Use the sink normally for the rest of the day. Before bed, look under the sink with a flashlight to check for slow drips around the valve connections. If you see any water, tighten that fitting by a quarter-turn and check again in the morning. Small weeps often stop on their own as the sealant sets, but persistent drips mean you need to tighten or reseal the connection.