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

The first and most critical step is to prevent any water flow to your work area. Locate the main water shutoff valve for your entire house. This is often found in a basement, crawl space, or utility closet near where the water service line enters the home. Turn the handle or lever clockwise until it stops to completely shut off the water. Next, relieve pressure in the plumbing system by opening a faucet on the lowest level of your home (like a basement sink or outdoor spigot) and letting it run until the water stops. Back at your work area, place a small bucket directly under the angle stop you are replacing and lay down several old towels to catch any residual water that will spill out during the process. Finally, gather all the tools and your new angle stop so they are within arm's reach.

Now you will disconnect the flexible supply line that runs from the top of the angle stop to the faucet. This line is attached with a smaller compression nut. Grip the body of the angle stop with a pair of channel-lock pliers or an adjustable wrench to keep it from moving. Use a second adjustable wrench to grip the nut on the supply line. Turn the wrench on the nut counter-clockwise to loosen it. Once it breaks free, you should be able to unscrew it the rest of the way by hand. As you detach the line, be ready for a small amount of water to drain out into the bucket you placed earlier. Tuck the disconnected supply line out of the way.

This step requires careful application of force. You will use two large wrenches to remove the old valve from the copper pipe stub-out. Place one wrench (a pipe wrench or large channel-locks work well) on the body of the valve itself, positioned to prevent the valve from turning. Place your second wrench (an adjustable wrench is good) on the large compression nut that is right against the wall or escutcheon plate. Turn this nut counter-clockwise. It may be very tight and require significant force to 'break' loose. Once it breaks free, continue to unscrew the nut. Once the nut is fully loosened, you can slide the entire old valve assembly off the end of the copper pipe.

With the old valve removed, you will see the old compression nut and a small brass ring, the ferrule, still on the copper pipe. Slide the old nut off. The ferrule is often compressed tightly and can be difficult to remove. The best tool for this is a ferrule puller, which safely pulls it off without damaging the pipe. If you don't have one, you can try to carefully cut a slot in the ferrule using a mini-hacksaw or a Dremel tool with a cutting wheel. Be extremely careful not to cut into or score the soft copper pipe underneath. Once you've cut almost all the way through, you can use a flat-head screwdriver to pry it open and pop it off. After the old ferrule is removed, use a piece of emery cloth or fine-grit sandpaper to thoroughly clean the last inch of the copper pipe. It should be smooth, shiny, and free of any burrs or old sealant.

Take your new quarter-turn angle stop and its components. First, slide the new compression nut onto the cleaned copper pipe, ensuring the threaded end faces outwards, away from the wall. Next, slide the new brass ferrule onto the pipe. The tapered end of the ferrule should face away from the wall, towards the end of the pipe where the valve will sit. Now, push the body of the new angle stop firmly onto the end of the pipe. It should slide over the pipe and butt up securely against the ferrule. Slide the compression nut forward and thread it onto the valve body by hand. Tighten it as much as you can with your fingers.

With the new valve hand-tightened, it's time to create the permanent, watertight seal. As before, you will use two wrenches. Use one wrench (channel-locks or adjustable) to hold the new valve body steady, ensuring its outlet is pointing in the correct direction (usually straight up towards the faucet connection). Use your second wrench to tighten the compression nut. Follow the manufacturer's instructions, but a general rule is to tighten the nut one-half to one full turn past the point where it was hand-tight. You will feel the ferrule compress and bite into the copper. The goal is to be tight enough to seal, but not so tight that you damage the pipe or valve. Do not over-tighten.

First, ensure the new angle stop is in the 'off' position (the handle should be perpendicular to the pipe for a quarter-turn valve). Re-attach the faucet supply line to the top outlet of the new valve. Hand-tighten the nut, then give it a gentle quarter-turn with an adjustable wrench. Now, go back to your main water shutoff valve and turn it on slowly to re-pressurize your home's pipes. Return to the sink and carefully inspect the new valve, especially around the large compression nut at the wall. Use a dry paper towel to wipe the connection; it will make even the smallest drop of water visible. If there are no leaks, slowly open the new angle stop by turning its handle counter-clockwise. Once open, check all connections again for leaks: the main connection at the wall and the supply line connection. Finally, turn on the faucet to test flow and check for any drips under the sink. Dry everything thoroughly and monitor for the next hour.