A phone line can only function properly when it is an independent circuit and not touching any other phone lines. If it comes into contact with another, it will stop functioning properly. You can use the ‘Continuity’ setting on your multimeterat the network interface device that you can find on the exterior wall of your home. If you are unsure of what to do, you can check out https://websitepromoter.co.uk/how-to-test-a-phone-line-without-a-phone/ for more information and follow the steps below:

• Disconnect anything that may be connected to your telephone jack, as you want the phone line free for testing.
• Find the network interface box called NID, which is usually grey in color and installed by the telephone company on an exterior wall near the electrical meter. This is where your phone lines are connected to the wiring loop of the phone company. Contact your phone company to find the exact location of the box, if you cannot find it.
• The NID has screws labeled ‘Customer Access’ that you can unscrew for removing the cover.
• Disconnect the phone lines that you want to test and they will be ready for testing. Give it a minute before beginning testing, as the electricity in the lines needs to dissipate.
• Make sure your multimeter is at its continuity setting, which is usually marked by a sound wave symbol.
• Take the tips of the digital multimeter leads and touch them together. The multimeter will show a reading on the screen and give off a beeping noise.
• Connect one of the leads to one phone wire and the second to a different one. The phone lines are not touching if the multimeter doesn’t detect any continuity. If it does, it means the phone lines are touching and will not function properly.