How to Install a New Hot Water Line Under a Sink


Hot and cold water lines under the sink are usually replaced when new faucets are installed. If the hot water line needs to be replaced due to wear, then it may be a good idea to replace the cold line as well. The lines are not expensive and you can find them at hardware stores. They attach with two nuts. When you set out to install a new hot water line, you may find it’s more difficult to get the old one off than to put on the new one.

Things You'll Need

  • New water lines
  • Plumbing tape
  • Adjustable wrench
  • Adjustable pliers
  • Oil or spray lubricant
  • Bucket
  • Stainless steel pad

How to Install a New Hot Water Line Under a Sink

  • Identify the hot water line. Chances are you know which is the hot water line, if you intend to replace it exclusively. If not, find it by turning on the hot water. Touch the lines under the sink to see which one of them gets warm.

  • Turn the water supply off. The water lines run from the under side of the faucet to a valve on the wall or the floor of the cabinet. Turn the valve clockwise by hand until it firmly stops.

  • Remove the old line. Place a bucket under the faucet connection. Hold nut on the faucet supply tube with an adjustable wrench, while turning the nut on the supply line counterclockwise. For any nut that won’t turn, apply oil or lubricant spray and let it soak for ten minutes. Use adjustable pliers to loosen the nut connected to the valve.

  • Clean and prepare the threads. Rub away all dirt and corrosion from the threads with a stainless steel pad. Do this on the faucet supply tube and the valve. Wrap plumbing tape around both sets of threads in a clockwise direction three times. Pull the tape tightly against the wrap until it snaps

  • Flush and connect the new lines. Place one end of your new line against a working faucet and flush water through it for about twenty seconds. Then connect the nuts to the taped threads at the faucet supply tube and the valve. Make the connects firm with adjustable pliers.

  • Check for leaks. Turn the water supply back on by turning the valve counter clockwise until it stops. Look at both connections of the new line to see if there are any leaks. Turn the faucet on and look again.

Tips & Warnings

  • Be aware that water may splash out of the line when you loosen the first nut. Dirt and particles of corroded metal may be in the water. Do not let it splash into your eyes.

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