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

The first and most critical step is to prevent water from flowing to the work area. Locate your home's main water shutoff valve, which is often found in the basement, a crawl space, or on an exterior wall. Turn the valve clockwise until it is fully closed. To confirm the water is off and to relieve pressure, go to the lowest faucet in the house (like a basement sink) and the faucet you are working on, and open both the hot and cold taps. Let the water drain until it stops flowing. Place a small bucket and some rags under the angle stop you will be replacing to catch any remaining water.

The faucet supply line is the flexible or rigid tube that runs from the angle stop up to the faucet. Using an adjustable wrench or basin wrench, carefully loosen the compression nut that connects this supply line to the top or side outlet of the angle stop. Turn the nut counter-clockwise. Hold the body of the angle stop with your other hand or a pair of channel lock pliers to prevent it from turning while you loosen the nut. Once loose, unscrew it by hand and gently pull the supply line away from the valve.

Now you will remove the entire valve assembly. Place one adjustable wrench on the main body of the angle stop. Place a second adjustable wrench or pipe wrench on the pipe or nut behind it for counter-torque. This is crucial to avoid damaging the pipe in the wall. Hold the second wrench steady and use the first wrench to turn the compression nut on the angle stop counter-clockwise. It may require significant force to break it loose. Once it's loose, you should be able to unscrew the entire valve from the compression nut and slide it off the copper pipe.

With the valve body removed, the old compression nut and the brass compression ring (ferrule) will remain on the copper pipe. Slide the old nut off. The ferrule is often stuck firmly in place. Sometimes you can carefully pry it off with two screwdrivers or by gripping it with pliers and twisting. If it won't budge, the safest method is to use a dedicated ferrule puller tool. As a last resort, you can very carefully cut a slot in it with a small hacksaw or rotary tool, being extremely careful not to cut into the copper pipe itself, and then split it off with a flathead screwdriver.

Once the old fittings are off, inspect the end of the copper pipe. It must be clean, smooth, and perfectly round for the new valve to seal. Use some emery cloth or fine-grit sandpaper to clean off any corrosion, old plumber's putty, or burrs from the last inch of the pipe. Wipe it clean with a dry rag to remove any dust or debris. The surface where the new ferrule will sit must be pristine.

Take your new angle stop and unscrew the compression nut. Slide the new nut onto the cleaned copper pipe first, with its threads facing towards you. Then, slide the new brass ferrule onto the pipe, with its tapered end facing away from you (towards the wall). Push the new angle stop body onto the pipe until it seats firmly against the ferrule. Slide the nut up to the valve body and hand-tighten it. Now, using two wrenches again (one for counter-torque), tighten the compression nut an additional one-half to three-quarters of a turn past hand-tight. Do not overtighten, as this can crush the ferrule and pipe, causing a leak.

With the new angle stop securely installed, it's time to reconnect the faucet supply line. Align the supply line with the outlet port on the new valve and thread the compression nut on by hand. Make sure it's not cross-threaded. Once hand-tight, use an adjustable wrench to snug it up, typically another quarter to half turn. Again, hold the valve body with your other hand or pliers to prevent it from moving.

The final step is to check your work. Ensure the new angle stop is in the closed position (for a quarter-turn valve, the handle will be perpendicular to the pipe). Go back to your main water shutoff and turn it on slowly, counter-clockwise, until it is fully open. Return to the sink and carefully inspect both connections on the new angle stop (the one at the wall and the one to the supply line) for any drips. Use a dry paper towel to wipe the connections; it will make even the smallest drop of water visible. If there are no leaks, slowly turn the handle on the new angle stop to the open position. Then, check for leaks again. Finally, turn on the faucet to let any air out of the lines and check for proper flow.