Step-by-step fix
Step 1: Make sure the hot supply line is the problem
- Open the faucet and compare hot flow to cold flow.
- Look under the sink while the hot side is running and check the hot supply line for drips, corrosion, bulges, sharp bends, or a crushed braided section.
- Feel along the line for obvious kinks or spots where stored items have been pressing against it.
- If the issue is a leak, dry the line and fittings first, then run only hot water and watch for fresh moisture at the line or its connections.
If it works: You have a clear reason to replace the hot supply line, such as a leak, visible damage, or a restricted line causing weak hot flow.
If it doesn’t: If both hot and cold flow are weak, or the leak is coming from the faucet body or shutoff valve instead of the line, this is probably the wrong repair path.
Stop if:- The shutoff valve itself is leaking from the stem or body.
- The cabinet, sink base, or surrounding wood is soft, swollen, or badly water-damaged.
- You cannot tell where the leak starts because multiple parts are wet at once.
Step 2: Shut off the hot water and set up the work area
- Clear out the cabinet so you can reach the shutoff valve and faucet connection comfortably.
- Place a towel and bucket under the hot supply line.
- Turn the hot-side shutoff valve clockwise until it stops.
- Open the kitchen faucet to relieve pressure, then move the handle to the hot side until water flow stops or slows to a drip.
If it works: The hot water is off, pressure is relieved, and the area under the sink is protected from drips.
If it doesn’t: If the hot shutoff valve will not close fully, you may need to shut off water to the home before removing the line.
Stop if:- The shutoff valve will not turn, starts leaking heavily when touched, or will not stop the water enough to work safely.
Step 3: Remove the old hot supply line
- Use a wrench to loosen the nut at the shutoff valve while holding the valve steady if needed.
- Disconnect the other end from the faucet hot inlet or faucet shank.
- Let the remaining water drain into the bucket.
- Remove the old line completely and keep it nearby so you can compare length, thread size, and end style with the replacement.
- Wipe both connection points clean so the new line can seat properly.
If it works: The old hot supply line is out and both connection points are clean and easy to inspect.
If it doesn’t: If one end will not break loose, apply steady pressure and improve your tool angle rather than forcing the tubing to twist.
Stop if:- The faucet inlet, shutoff valve outlet, or mounting hardware starts twisting with the line.
- Threads are badly corroded, cross-threaded, cracked, or partly broken.
Step 4: Match and install the new supply line
- Compare the new line to the old one for overall length, end sizes, and connection style.
- Start the faucet-end connection by hand first so you do not cross-thread it.
- Start the shutoff-valve end by hand next.
- Route the line in a smooth curve without a kink, twist, or hard bend.
- Tighten both ends snugly with a wrench, but do not overtighten.
- Make sure the line is not rubbing on a sharp cabinet edge or getting pinched by stored items.
If it works: The new hot supply line is installed with hand-started threads, a smooth route, and snug connections at both ends.
If it doesn’t: If the nut will not thread on smoothly by hand, back it off and recheck the fit before tightening again.
Stop if:- The replacement line does not match the old line's connection type or size.
- The line must be forced into place to reach, or it kinks when routed normally.
Step 5: Turn the water back on and check for leaks
- Close the faucet.
- Slowly open the hot-side shutoff valve.
- Watch both ends of the new line as pressure returns.
- Wipe each connection dry with a rag, then check again for fresh moisture.
- If you see a small drip, tighten that connection slightly and recheck.
If it works: The line holds pressure without visible drips at either connection.
If it doesn’t: If a connection still seeps after a slight retightening, shut the water back off and inspect for a bad fit, crooked threads, or the wrong replacement line.
Stop if:- A fitting sprays, the shutoff valve leaks from the body, or water is escaping fast enough to damage the cabinet.
Step 6: Confirm the repair in normal use
- Run hot water at the faucet for a minute and confirm the flow is steady.
- Check under the sink again while the hot water is running and again a few minutes after shutting it off.
- Make sure the new line stays dry and does not shift, rub, or kink as the faucet is used.
- Put items back in the cabinet carefully so nothing presses against the new line.
If it works: Hot water flow is normal and the new supply line stays dry during and after real use.
If it doesn’t: If hot flow is still weak with a new line installed, the restriction may be in the shutoff valve, faucet inlet, or faucet cartridge rather than the supply line.
Stop if:- You still have active leaking, recurring moisture, or signs that another plumbing part is failing.
Replacement Parts
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FAQ
How do I know the hot supply line is bad?
Common signs are a visible leak, corrosion at the fittings, a crushed or kinked line, or weak hot flow when the cold side still runs normally.
Do I need thread tape on a faucet supply line?
Usually no on the supply line nuts themselves. These connections typically seal at the fitting, not on the threads. Match the replacement line correctly and start the threads by hand.
Can I replace just the hot line and leave the cold line alone?
Yes, if only the hot line is leaking or restricted and the cold line is in good shape. If both lines are old and access is easy, some homeowners replace both while they are already under the sink.
What if the shutoff valve will not close all the way?
Do not remove the line with water still feeding it. Shut off water to the home first, or address the faulty shutoff valve before continuing.
Why is hot water still weak after I replaced the line?
The restriction may be elsewhere, such as the shutoff valve, faucet inlet, or faucet cartridge. The new line only fixes the problem if the old line was the actual bottleneck.