How to Replace a Leaky Angle Stop (Shutoff Valve) Under Your Sink

The first and most critical step is to completely shut off the water to your home. Locate your home's main water shutoff valve, which is typically found in the basement, a crawl space, or a utility closet near where the main water line enters the house. It will have either a wheel-style handle or a lever handle. Turn the handle clockwise until it is fully closed. To verify that the water is off, go to the sink you will be working on and turn on the faucet. The water flow should slow to a trickle and then stop completely. Leave the faucet open.

With the water off, open both the hot and cold handles on the faucet above the angle stop you are replacing. This action relieves any remaining water pressure in the pipes. Place a small bucket directly under the old angle stop to catch water that will drain from the line. Arrange several old towels or rags around the bucket to protect your cabinet from any spills.

Using an adjustable wrench, grip the nut that connects the faucet supply line (the flexible or rigid tube going up to the faucet) to the outlet of the leaky angle stop. Turn the nut counter-clockwise to loosen it. Hold the valve body with your other hand to prevent it from twisting. Once the nut is loose, you should be able to unscrew it by hand. Pull the supply line away from the valve and tuck it out of the way. A small amount of water will drain out into your bucket.

This step requires two wrenches. Use one adjustable wrench or a pair of channel-lock pliers to grip the body of the old angle stop firmly. This is crucial to prevent the copper pipe from twisting, kinking, or breaking inside the wall. With a second adjustable wrench, grip the large compression nut that connects the valve to the pipe stub-out. Turn this nut counter-clockwise. It may be very tight and require significant force. Once you break it loose, you can unscrew it the rest of the way by hand. Slide the old valve straight off the pipe.

Once the old valve is off, inspect the copper pipe. You will see the old compression nut and a brass compression ring called a ferrule. Slide the old nut off. The ferrule must also be removed for a proper seal with the new valve. It can be stubborn. You may be able to carefully cut a slit in it with a utility knife (without cutting into the copper pipe) and pry it off. A dedicated ferrule puller tool is the safest method. Once the old parts are off, use emery cloth or fine-grit sandpaper to thoroughly clean the last inch of the copper pipe. It should be smooth and shiny, free of any corrosion, scale, or scratches. Wipe it clean with a dry rag.

Take your new quarter-turn angle stop. Ensure the valve handle is in the 'off' position (perpendicular to the valve outlet). Unscrew the compression nut from the valve body. Slide the new nut onto the prepared copper pipe, with the threads facing you. Then, slide the new brass ferrule onto the pipe, ensuring its tapered end points towards the end of the pipe where the valve will sit. Push the new valve body firmly onto the pipe until it bottoms out against the ferrule. Slide the nut up and hand-tighten it onto the valve body. Now, use two wrenches again: one to hold the valve body steady and one to tighten the compression nut. Tighten the nut about one-half to one full turn past hand-tight. Do not over-tighten.

Align the faucet supply line with the outlet on the new angle stop. Thread the supply line's compression nut onto the valve's outlet by hand. Make sure it threads on smoothly to avoid cross-threading. Once it is hand-tight, use an adjustable wrench to give it another quarter to half-turn to snug it up. This connection does not need extreme force; the rubber cone seal inside the supply line nut creates the seal.

This is the moment of truth. Go back to the main water shutoff valve and turn it on slowly, opening it counter-clockwise all the way. Listen for any sounds of rushing water. Return to the sink and use a flashlight to meticulously inspect the new angle stop. Look for any signs of moisture or drips at both connections: where the valve meets the wall pipe and where the supply line connects to the valve. Use a dry paper towel to wipe down all connections, as this will make even the tiniest leak visible. If everything is dry, slowly turn the handle on the new angle stop a quarter-turn to the 'on' position (handle will be parallel to the outlet). Water should now be flowing to the faucet. Check the faucet for normal operation and perform one final leak check on all connections.