How To Fix A Leaking Shut-Off Valve Under The Kitchen Sink

Perhaps you open your kitchen cabinet to put something in there for storage. However, you’re assaulted by a musty smell once you open the door. Upon further investigation, you discover the shut-off valve is leaking all over the cabinet beneath the sink. There’s substantial water damage to the cabinet, causing bubbles on the bottom. 

While the water damage in the cabinet is one thing, we need to address the culprit causing the problem first: the leaking shut-off valve. We might’ve missed the mark with our little story here – maybe you happened to notice the leak before it caused significant damage (lucky you!), but you get the point. 

Fixing a leaking shut-off valve isn’t tricky, but it’ll take some time. Here’s how to do it. 

Why Is My Shut-Off Valve Leaking Under The Sink?

Like most products, plumbing shut-off valves wear out over time. Many times, these valves go years without being turned on and off. The lack of use doesn’t bode well for the valve, especially after many years.

Inside the valve, there are neoprene washers that help turn the flow of water completely off or on. Over time, these valves wear out, becoming brittle or covered in mineral deposits. When this happens, the washer loses its ability to seal properly, causing the leak you see underneath your sink (or anywhere else there is a shut-off valve).

How Do You Fix A Leaking Water Shut-Off Valve?

A leaking shut-off valve is a nuisance, regardless of where it is. However, a leaky valve beneath the sink can quickly become a nightmare. The kitchen sink is often used frequently throughout the day in most homes, so the leak can quickly create issues. If left unchecked, the leak will lead to water damage to the cabinet below. 

Here’s how to fix the problem:

Dry The Area

Before you get too carried away, ensure it isn’t excess water from a recent repair. For example, maybe you just installed a new faucet or switched out the supply lines. You may have had wet hands when you worked with the assembly, or maybe there was a leak close to the faucet that you fixed. 

These occurrences can cause there to be water near the supply lines. So, before taking things apart, ensure it isn’t just excess water. Here’s what you need:

  • Towel
  • Flashlight 

Dry the area thoroughly with a towel, ensuring you clean up any water near and on the supply lines. After you dry the area, monitor it closely with a flashlight for the next thirty minutes. You don’t need to sit there staring at it; just check it every five minutes or so for water formation on or around the valve. 

If new water arises, there’s a leak that you need to fix. 

Use Plumber’s Tape

Replacing the valve is usually your best bet, especially once you determine the leak is due to faulty valves. However, if you don’t want to place the entire valve, you can always do a bandaid fix with plumber’s tape. 

Here’s what tools and materials you need:

  • Plumber’s tape
  • Bucket
  • Towel
  • Wrench
  • Flashlight 

You’ll need to turn off the water at the main water supply. Once the water is off, place a towel and a bucket underneath the valve. Next, remove the water inlet valve with a wrench. Clean the valve to remove any corrosion, then wrap all the threads with plumber’s tape. 

Reinstall the inlet valve and check your handiwork. Turn on the water and monitor the area for leaks for thirty minutes. If there aren’t any leaks, you’re good to go. However, you’ll need to replace the valve if the leak persists. 

Remember, this isn’t a long-term fix. While it may work for a while, the issue might pop up again later. 

Replace The Valve

Sometimes, replacing the valve is your only option. Luckily, it’s a straightforward process. Bonus: replacement shut-off valves are pretty cheap! Here’s what you’ll need:

  • Bucket
  • Towel
  • Flashlight
  • Wrench
  • Replacement valve

To start, turn off the water at the main shut-off valve. Position the towel and bucket underneath the shut-off valve. Bleed the excess water from the water supply lines by opening the kitchen faucet. Once the water stops flowing, disconnect the water supply line from the shut-off valve you’re replacing. 

Remove the old shut-off valve with a wrench and set it aside. If you haven’t already, pick up a replacement water shut-off valve. You can take the old valve to the hardware store with you if you aren’t sure what type you need. 

Make sure the new shut-off valve is in the OFF position, then install it. Make sure you install it at the right angle so it creates a tight seal and threads correctly. Don’t wrap the threads on the valve stem with plastic plumber’s tape or pipe dope, as this can damage the inside of the shut-off valve. 

Hook up the water supply line to the new shut-off valve, then turn the water back on at the water main. Turn on the water at the shut-off valve and check your handiwork. Watch for leaks, checking back periodically with a flashlight. 

If everything looks good, you’ve fixed your leak!

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