How to Replace Shut-Off Valves Under the Sink

Shut-off valves under your sink are the gatekeepers between your home's water supply and a potential flood. When they weep, stick, or fail to close completely, replacing them is the only real fix—and it's a job you can handle yourself. The work involves some basic unscrewing, a little plumber's tape, and the confidence to know that if something goes wrong, you can still reach the main shut-off in your basement or meter box. This guide assumes you're working with standard compression or ball valves, the most common types found under kitchen sinks. If you see something unfamiliar—cartridge valves, for instance—take a photo and confirm the type before you start.

1. Shut Off Water Now. Locate your main shut-off valve. It's usually in the basement near the water meter, or outside in a meter box. Turn the handle clockwise until it stops. If you have a gate valve (a wheel handle), turn it slowly and completely. Do not force it. Run a faucet upstairs to confirm the water is off before you proceed.
2. Catch the Drips. Spread old towels on the floor and under the pipes. Even though the system should be empty after you turn off the main valve, water pools in low spots. Have a bucket ready as well.
3. Spot the Culprit. Look under the sink. You'll see two shut-off valves: one on the hot water line (usually on the left, connected to the hot water supply) and one on the cold water line (usually on the right, connected to the cold water supply). Locate the valve that's leaking, stuck, or non-functional. If both are old, replace both now rather than do this job twice.
4. Release the Supply Line. Using two adjustable wrenches or one wrench and one pipe wrench, grip the valve body with one tool to keep it steady, and turn the nut connecting the supply line to the valve counterclockwise with the other. Work slowly. Once the nut is loose enough by hand, unscrew it completely and slide the supply line away from the valve. Expect water to drip—this is normal.
5. Unthread the Old Valve. The valve screws onto a short pipe stub that comes down from the sink. Use a pipe wrench to grip the stub from above (under the sink) to keep it from turning, and use another wrench on the valve nut below to turn it counterclockwise. This stub is delicate—do not let it spin. Once the valve is loose, unscrew it by hand and remove it completely.
6. Strip the Threads Clean. Wipe the exposed threads on the sink stub with a clean, dry rag. Remove any old tape, debris, or mineral deposits. The stub should look clean and bare. Do not use steel wool or abrasives that might damage the chrome finish if the stub is exposed.
7. Seal the Threads. Tear off about 3 feet of plumber's (PTFE) tape. Starting just below the threads, wrap the tape around the stub in a clockwise direction, overlapping each pass by half the tape's width. Make 3-4 complete passes, keeping the tape tight and smooth. The goal is a thin, even layer with no wrinkles.
8. Thread the New Valve. By hand, screw the new valve clockwise onto the taped stub. Turn it until it's snug—you should feel slight resistance. Do not use a wrench yet. Once hand-tight, use a pipe wrench to tighten an additional half-turn to three-quarters of a turn. Stop when you feel firm resistance. Overtightening will crack the stub.
9. Reattach Supply Line. Slide the supply line nut back onto the valve connection and hand-tighten. Use two wrenches—one to hold the valve body steady, one to tighten the nut clockwise—and snug it down. Tighten it firmly but not with all your strength; you're looking for snug, not bone-breaking.
10. Restore Water Flow. Go to your main shut-off and turn the handle counterclockwise slowly. As water flows back into the lines, air pockets may cause spitting or sputtering at faucets upstairs—this is normal. Once you hear steady flow, let it run for 30 seconds, then turn it off.
11. Check for Leaks. Turn on the faucet above the sink and let it run for 1-2 minutes. Watch the valve connection and the supply line connection below the sink for any drips or spray. If you see water, turn off the faucet, go back to the main shut-off, and tighten the leaking connection a quarter-turn. Repeat until dry.
12. Verify the Seal. With the faucet running, turn the handle on the new valve clockwise. The water should stop flowing. Turn the handle counterclockwise to restore flow. Repeat this two or three times to confirm smooth operation and a complete seal. If the valve leaks past the handle (water still flows when the handle is fully closed), the valve is defective and must be replaced.