Adjustable wrench
Use it for: To loosen and tighten the supply line nuts at the shutoff valve and faucet.
Shop adjustable wrenchesBathroom sink plumbing
How to Replace a Bathroom Sink Hot Water Supply Line
If the hot side supply tube is dripping, corroded, kinked, or wet around its fittings, replacing the bathroom sink hot water supply line is usually a straightforward fix.
Most bathroom sink supply lines connect the hot shutoff valve to the faucet with simple threaded fittings. The job goes smoother if you confirm the leak is really coming from the line or its connections, then replace it with the same length and matching ends without over-tightening.
Before you start: Match the line length, end sizes, and connection type before ordering.
Safety first
- Hot water in the line can still drain out after the valve is closed, so use a bucket and open the faucet first.
- Support the shutoff valve while loosening stubborn fittings so you do not twist the pipe in the wall.
- Do not force mismatched threads or over-tighten fittings, which can damage the valve or faucet connection.
Tools you may need
Small bucket or bowl
Use it for: To catch the water left in the line when you disconnect it.
Find a small catch bucket
Towel or rag
Use it for: To protect the cabinet floor and wipe fittings dry for leak checks.
Shop absorbent shop towels
Flashlight
Use it for: To see the valve, faucet shank, and any slow drips under the sink.
Find a work flashlight
Tape measure
Use it for: To match the replacement line length before installation.
Shop tape measuresAs 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 problem
- Open the cabinet and dry the hot shutoff valve, the supply line, and the faucet connection with a towel.
- Run the hot water for a minute, then shut the faucet off and watch closely with a flashlight.
- Look for water forming on the line itself, at the lower nut on the shutoff valve, or at the upper nut where the line meets the faucet.
- Check whether the line is visibly corroded, kinked, rubbed through, or stained from past leaking.
If it works: You have traced the leak or damage to the hot water supply line or one of its end connections.
If it doesn’t: If the water is coming from the faucet body, drain assembly, shutoff valve stem, or the wall, this is not the right repair path.
Stop if:
- The shutoff valve body is leaking or badly corroded.
- The cabinet, wall, or floor shows swelling, rot, mold, or hidden water damage.
- You cannot clearly tell where the leak starts.
Step 2: Shut off the hot valve and relieve pressure
- Turn the hot water shutoff valve clockwise until it stops.
- Open the faucet to relieve pressure and let the remaining hot water drain out.
- Place a bucket or bowl under the supply line and lay down a towel under the work area.
- If the hot shutoff valve does not fully stop the water, close the home's main water supply before continuing.
If it works: Water flow has stopped and the line is ready to disconnect with only a small amount of residual water left inside.
If it doesn’t: If water keeps running from the hot side after the valve is closed, use the main shutoff and plan on addressing the faulty valve too.
Stop if:
- The shutoff valve will not close and you cannot shut off water at the main.
- The valve handle feels like it may break or the valve starts leaking heavily when touched.
Step 3: Remove the old hot water supply line
- Use one wrench to hold the shutoff valve steady if needed and another to loosen the supply line nut at the valve.
- Loosen the upper connection at the faucet shank or faucet inlet and remove the old line.
- Let the remaining water drain into the bucket.
- Compare the old line's length, end sizes, and connection style before setting it aside.
If it works: The old hot water supply line is out and you know what size and style the replacement needs to match.
If it doesn’t: If the nut is stuck, apply steady pressure and avoid twisting the valve or faucet connection out of position.
Stop if:
- The shutoff valve or faucet connection starts turning with the nut.
- Threads on the valve or faucet are damaged, split, or badly corroded.
Step 4: Install the new supply line without kinking it
- Position the new line so it reaches naturally without stretching, sharp bends, or rubbing on the cabinet.
- Start the upper connection by hand first to avoid cross-threading, then start the lower connection by hand.
- Tighten both ends snugly with a wrench, using controlled turns instead of forcing them.
- Keep the line in a gentle curve rather than a tight loop or twist.
If it works: The new line is fully connected, hand-started correctly, and routed cleanly without strain.
If it doesn’t: If the line will not thread on easily by hand, remove it and recheck the end size and connection type before tightening again.
Stop if:
- The replacement line is too short, too long to route safely, or has the wrong fittings.
- The threads will not start cleanly by hand.
Step 5: Turn the water back on and check for leaks
- Close the faucet if it is still open.
- Slowly open the hot shutoff valve and watch both supply line connections as pressure returns.
- Wipe both fittings dry, then run the hot water for a minute and shut it off again.
- Check the line and both ends for drips, sweating, or seepage.
- If needed, tighten a leaking connection slightly and recheck.
If it works: Both connections stay dry while the hot water is running and after the faucet is shut off.
If it doesn’t: If a fitting still seeps after a small retightening, shut the water back off and inspect for a mismatched line, crooked connection, or damaged threads.
Stop if:
- A connection leaks more as you tighten it.
- The shutoff valve or faucet connection begins leaking from a different point.
Step 6: Make sure the repair holds in normal use
- Use the sink normally several times over the next few hours, especially with hot water.
- Check under the sink after each use and again later when the line has been sitting under pressure.
- Run your fingers around the upper and lower fittings and look for fresh moisture on the towel or cabinet floor.
- Remove the bucket and cleanup only after everything stays dry.
If it works: The new hot water supply line stays dry during use and while sitting under pressure, confirming the repair held.
If it doesn’t: If moisture returns later, dry everything again and pinpoint whether it is coming from the new line, the shutoff valve, or the faucet itself.
Stop if:
- You find recurring moisture that is clearly coming from the wall, valve body, or faucet rather than the new line.
- The cabinet shows ongoing water damage even after the line replacement.
Replacement Parts
Find a bathroom 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
- The hot shutoff valve opens and closes normally.
- The new line is not kinked, twisted, or rubbing on sharp cabinet edges.
- Both supply line connections stay dry while hot water is running.
- The area under the sink remains dry after several normal uses.
FAQ
How do I know the supply line is bad and not the faucet?
Dry everything first, then run and shut off the hot water while watching closely. If water forms on the tube or at its end nuts, the supply line or its connections are the likely cause. If water starts higher up on the faucet body, the faucet is more likely the problem.
Can I replace just the hot water supply line?
Yes. If only the hot side line is leaking or damaged, you can replace that line by itself as long as the new one matches the existing connection sizes and length.
Do I need thread seal tape on a bathroom sink supply line?
Usually no for the supply line nuts themselves. These connections are typically designed to seal at the fitting, not on the threads. The important part is using the correct line and starting the threads cleanly by hand.
What length supply line should I buy?
Match the old line or measure the route from the hot shutoff valve to the faucet connection. Choose a length that reaches in a gentle curve without stretching or looping tightly.
Why is it still leaking after I replaced the line?
The most common causes are a crooked connection, wrong end size, damaged threads, or a leak that is actually coming from the shutoff valve or faucet. Dry the area and watch closely to find the true source before tightening more.