Adjustable wrench
Use it for: To loosen and tighten the supply line nuts at the shutoff valve and faucet connection.
Shop adjustable wrenchesKitchen sink plumbing
How to Replace a Kitchen Sink Hot Water Supply Line
To replace a kitchen sink hot water supply line, confirm the hot-side line is the source of the leak or restriction, shut off the hot water stop valve, remove the old line, install a matching replacement, and test both connections under running hot water.
This is a straightforward under-sink repair if the shutoff valve works and the fittings come apart cleanly. The key is using the correct length and connection size, then tightening just enough to seal without damaging the valve or faucet shank.
Before you start: Match the line length, end sizes, and connection type before ordering.
Safety first
- Hot water in the line can be warm enough to surprise you, so open the faucet slowly and keep a bucket underneath before disconnecting anything.
- Support the shutoff valve while loosening or tightening the line so you do not stress the pipe in the wall.
- Do not force stuck fittings hard enough to twist the valve, faucet shank, or supply pipe.
Tools you may need
Channel lock pliers
Use it for: To hold the valve body or faucet shank steady while you turn the supply line nut.
Shop tongue and groove pliers
Small bucket or pan
Use it for: To catch the water left in the line when you disconnect it.
Find a drain pan or bucket
Towel or rag
Use it for: To wipe fittings dry so you can spot fresh drips during testing.
Shop shop towels
Flashlight
Use it for: To see the back side of the shutoff valve and faucet connection under the sink.
Find a work flashlightAs an Amazon Associate I earn from qualifying purchases. Repair Riot may earn a commission at no extra cost to you.
Step-by-step fix
Step 1: Confirm the hot water supply line is the right repair
- Empty the cabinet under the sink so you can see the shutoff valve, the hot-side supply line, and the bottom of the faucet clearly.
- Run the hot water and look underneath with a flashlight.
- Check for drips, corrosion, bulging, kinks, or a wet braided line on the hot side only.
- Wipe the line and both connection points dry, then run hot water again to see where fresh moisture starts.
- Make sure the leak is not coming from the faucet body, sprayer hose, drain, or the shutoff valve stem.
If it works: You have confirmed the hot water supply line or one of its end connections is the source of the problem.
If it doesn’t: If the water is coming from the shutoff valve itself or from the faucet body, fix that part instead before replacing the line.
Stop if:
- The shutoff valve is heavily corroded, loose at the wall, or leaking from the valve body.
- You find cabinet damage, mold, or hidden water damage that needs a larger repair.
Step 2: Shut off the hot water and relieve pressure
- Turn the hot water shutoff valve clockwise until it stops.
- Open the faucet to the hot side to relieve pressure and drain the line.
- Place a bucket or pan under the shutoff valve and line.
- Leave the faucet open for a moment until the flow slows to a drip.
If it works: The hot-side line is depressurized and ready to remove with only a small amount of water left inside.
If it doesn’t: If hot water keeps flowing strongly, the shutoff valve is not closing fully and the repair may need to include the valve.
Stop if:
- The shutoff valve will not close enough to stop the water.
- The valve handle breaks, the valve starts leaking, or the valve body twists when touched.
Step 3: Remove the old hot water supply line
- Use one tool to hold the shutoff valve steady if needed and another to loosen the supply line nut at the valve.
- Disconnect the lower end first and let the remaining water drain into the bucket.
- Loosen the upper nut at the faucet connection and remove the old line completely.
- Compare the old line to the new one for length, end size, and connection style before installing anything.
- Wipe both connection points clean so the new line can seat properly.
If it works: The old line is out and you have confirmed the replacement matches the original setup.
If it doesn’t: If the new line does not match, take the old line with you and get one with the same connection type and a similar length without stretching or sharp bends.
Stop if:
- A fitting is seized so badly that the faucet shank or shutoff valve starts turning with it.
- The faucet connection threads or shutoff valve threads are cracked, stripped, or badly damaged.
Step 4: Install the new supply line
- Start the top connection by hand first so you do not cross-thread it.
- Start the bottom connection by hand at the shutoff valve.
- Route the line in a smooth curve without twisting, kinking, or pulling it tight.
- Tighten each connection snugly with a wrench while holding the valve or faucet connection steady if needed.
- Do not overtighten; the goal is a firm seal, not maximum force.
If it works: The new hot water supply line is installed with both ends threaded cleanly and routed without strain.
If it doesn’t: If a nut will not thread on smoothly by hand, back it off and realign it before tightening again.
Stop if:
- The line has to be forced into place because it is too short or the wrong shape.
- Any fitting cross-threads or the connection will not seat squarely.
Step 5: Turn the water back on and check for leaks
- Close the faucet.
- Slowly open the hot water shutoff valve while watching the lower connection.
- Check the upper faucet connection next.
- Wipe both fittings dry with a towel, then wait a minute and look again for fresh moisture.
- If you see a small drip, tighten that connection a little more and recheck.
If it works: The valve is back on and both supply line connections stay dry at rest.
If it doesn’t: If a connection still drips after a small retightening, shut the valve back off, disconnect that end, and inspect the fit and threads again.
Stop if:
- Water sprays from a connection or the shutoff valve begins leaking from the body or stem.
- A slow drip continues even after the line is correctly seated and lightly retightened.
Step 6: Verify the repair under normal hot water use
- Run the hot water at the faucet for a few minutes so the line sees normal pressure and temperature.
- Watch the line while the water is running, then check again right after you shut the faucet off.
- Feel around both fittings with a dry finger or tissue to catch tiny leaks you might not see.
- Check the cabinet floor again after 15 to 30 minutes to make sure no delayed drips appear.
If it works: The new hot water supply line stays dry during use and after the faucet is shut off, so the repair is holding.
If it doesn’t: If moisture returns only during use, recheck the exact source because the faucet, sprayer hose, or shutoff valve may also be leaking.
Stop if:
- You still have leaking after reinstalling a correct replacement line.
- The hot water flow is still poor and the original problem was not caused by the supply line.
Replacement Parts
Find a kitchen sink hot water supply line on Amazon
Match the line length, end sizes, and connection type before ordering.
As an Amazon Associate I earn from qualifying purchases. Repair Riot may earn a commission at no extra cost to you.
Verify the repair
- Both connection points stay dry with the faucet off.
- No drips appear while hot water is running.
- The line is not kinked, twisted, or rubbing sharply against the cabinet.
- The cabinet floor stays dry after the sink has been used normally.
FAQ
How do I know which line is the hot water supply line?
Under most sinks, the hot shutoff valve is on the left and connects to the hot side of the faucet. If you are unsure, run warm water briefly and carefully feel which line warms up.
Do I need thread tape on a kitchen sink hot water supply line?
Usually no on the supply line nuts themselves. These connections typically seal at the fitting, not on the threads. Use the replacement line exactly as its connection style is designed to install.
How tight should the new supply line be?
Tight enough to seal without dripping, but not so tight that you damage the fitting. Start by hand, then snug it with a wrench. If it seeps, tighten a little more and test again.
Can I replace just the hot water supply line and leave the cold one alone?
Yes, if only the hot line is leaking or damaged and the cold line is in good shape. If both lines are old, corroded, or the same age, many homeowners replace both while access is open.
What if the shutoff valve will not close?
If the hot shutoff valve will not stop the water, the job may need to include replacing the valve or shutting water off upstream first. Do not continue if you cannot control the water safely.