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 supply to your entire home. Locate the main water shutoff valve, which is typically found in a basement, crawl space, or utility closet near where the main water line enters the house. Turn the valve handle clockwise until it stops. To drain the remaining water from the plumbing system, go to the lowest level of your home (like a basement sink or outdoor spigot) and open the faucet. Then, open the faucet at the sink where you'll be working to relieve any remaining pressure and drain the line. Place a bucket and towels directly under the angle stop you will be replacing to catch any residual water.

The angle stop is connected to the faucet via a flexible water supply line. Using an adjustable wrench or channel-lock pliers, loosen the coupling nut that secures this supply line to the top or side of the angle stop. Turn the nut counter-clockwise ('lefty-loosey'). You may need to hold the valve body steady with your other hand to prevent it from twisting. Once loosened, you can typically unscrew it the rest of the way by hand. Move the supply line out of the way.

Now you will remove the old valve from the copper pipe stub-out coming from the wall. This requires two wrenches. Use one wrench (e.g., a pipe wrench or large adjustable wrench) to grip the valve body securely to provide counter-torque. Use a second adjustable wrench to grip the large compression nut located behind the valve body. Turn the second wrench counter-clockwise to loosen the nut. This may require significant force if the valve is old. Once the nut is loose, unscrew it completely and slide it back on the pipe. The old angle stop should now pull straight off the copper pipe.

With the valve body removed, the old compression nut and the small brass ring, called a ferrule (or compression sleeve), will remain on the copper pipe. These must be removed. The ferrule is compressed onto the pipe and can be difficult to get off. The best tool for this is a compression sleeve puller, which neatly pulls the ferrule and nut off without damaging the pipe. Alternatively, you can carefully cut a slot in the ferrule with a small hacksaw or rotary tool, being extremely careful not to cut into the copper pipe itself, and then pry it open with a flathead screwdriver. Do not reuse the old nut or ferrule.

Once the old hardware is removed, thoroughly clean the end of the copper pipe stub-out. Use a piece of emery cloth or fine-grit sandpaper to polish the last inch of the pipe, removing any oxidation, old sealant, or burrs. The surface should be smooth and shiny. This ensures the new ferrule can create a perfect, watertight seal. Wipe the pipe clean with a dry rag to remove any dust or debris.

Take your new angle stop; it should come with a new compression nut and ferrule. First, slide the new compression nut onto the clean copper pipe, making sure the threads face outwards, towards you. Next, slide the new brass ferrule onto the pipe with its tapered end facing the end of the pipe (towards where the valve will go). Now, push the body of the new angle stop firmly onto the end of the pipe until it seats snugly against the ferrule. The pipe should go about 1/2 to 3/4 inch into the valve body.

Slide the compression nut up to the threads on the valve body and hand-tighten it as much as you can. Now, use your two wrenches again. Use one wrench as a backup to hold the valve body steady, preventing it from turning. Use the other wrench to tighten the compression nut an additional one-half to three-quarters of a turn. The goal is to compress the ferrule onto the pipe to create a seal, but not to overtighten it. Do not use plumber's tape or pipe dope on compression fittings.

With the new angle stop securely installed, re-attach the flexible faucet supply line to the valve's outlet port. Screw the coupling nut on by hand until it is snug. Then, use your adjustable wrench to give it a final quarter-turn to snug it up. This connection typically has a rubber gasket, so it does not require extreme force to seal.

The moment of truth. First, ensure the new angle stop is in the closed position and the sink faucet is also closed. Go back to your main water shutoff valve and turn it on SLOWLY. Turning it on too fast can cause a 'water hammer' effect that can damage pipes. Once the main is fully on, return to the sink. Carefully inspect the new angle stop, particularly around the compression nut and the supply line connection, for any signs of water. Use a dry paper towel to wipe every part of the connection; it will instantly reveal even the tiniest drip.

If there are no leaks with the valve closed, it's time for the final test. Slowly turn the handle on the new angle stop a quarter turn to the open position (the handle should be parallel to the pipe). Water will now flow to the faucet. Turn the faucet on and let it run for a minute, purging any air from the line. While the water is running, perform one last, thorough check for leaks around the valve, its stem, and both connections. If everything is dry, you have successfully replaced your angle stop. Clean up your tools and dry the area under the sink.