How to Replace an Under Sink Shutoff Valve

Step 1: Confirm the shutoff valve is the problem

1. Open the cabinet and dry the valve, supply line, and pipe stub-out so you can see where fresh water appears.
2. Turn the valve handle clockwise to close it, then run the faucet. If water keeps flowing strongly, the valve is not shutting off properly.
3. Check whether the leak is coming from the valve body, around the handle stem, or from the connection where the valve meets the pipe.
4. Look at how the valve connects to the pipe before buying parts. Common connection styles are compression, threaded, and push-to-connect.
5. Buy a replacement valve that matches the pipe size, connection type, and outlet size for the faucet supply line.

If it works: You know the valve itself is leaking or failing to shut off, and you have a matching replacement valve.

If it doesn’t: If the leak is actually from the faucet supply line or the faucet above, replace that part instead of the shutoff valve.

Step 2: Shut off the house water and relieve pressure

1. Turn off the main water supply to the home.
2. Open the sink faucet to relieve pressure and let the line drain down.
3. Place a bucket or shallow pan under the shutoff valve.
4. Disconnect the faucet supply line from the shutoff valve outlet and let any trapped water drain into the bucket.

Step 3: Remove the old shutoff valve

1. Hold the pipe steady with pliers if needed so you do not twist it in the wall.
2. For a compression valve, loosen the compression nut and slide the valve off the pipe.
3. For a threaded valve, turn the valve off the threaded stub-out while backing up the pipe or fitting so you do not stress the plumbing behind the wall.
4. If an old compression sleeve and nut are stuck and the new valve will not reuse them, remove them with a compression sleeve puller.
5. Wipe the exposed pipe clean so the new valve can seat properly.

Step 4: Install the new shutoff valve

1. Slide the new nut and ferrule onto the pipe first if you are installing a compression valve, then push the valve onto the pipe fully.
2. Thread the compression nut onto the valve and tighten it while holding the valve in the correct direction for the supply line.
3. If you are installing a threaded valve, start the threads carefully by hand to avoid cross-threading, then tighten while backing up the mating fitting.
4. Position the valve so the outlet lines up naturally with the faucet supply line instead of forcing the tubing sideways.
5. Reconnect the faucet supply line to the new valve outlet and snug the connection.

Step 5: Turn the water back on and check for leaks

1. Make sure the new shutoff valve is in the off position.
2. Slowly turn the main water supply back on.
3. Watch the new valve and the pipe connection closely as pressure returns.
4. Open the new shutoff valve slowly and let water flow to the faucet.
5. Dry every connection with a towel, then check again for fresh moisture around the inlet, outlet, and handle area.

If it doesn’t: If you see a slow drip at a compression connection, tighten it a little more while supporting the valve body, then dry and recheck.

Step 6: Verify the repair in normal use

1. Run both hot and cold water at the faucet for a minute, then shut the faucet off and watch the valve for several minutes.
2. Open and close the new shutoff valve a few times to confirm it actually stops water flow to the faucet.
3. Check the cabinet floor and the wall under the valve again after 15 to 30 minutes.
4. Look back once more later the same day for any slow seepage that only shows up after the line has been under pressure.

If it works: The shutoff valve works normally in real use and the cabinet stays dry.

If it doesn’t: If the valve works but a supply line connection seeps, disconnect and inspect that connection for a damaged washer or mismatched fitting.