Telephone lines not working


An analogue line NTE.

Analogue telephone lines are traditional telephone lines and can work with an ordinary telephone.

Unfortunately, there is no single consistent way in which analogue telephone lines are presented at customer premises and connected to telephone systems. Not all the ways that have been used in the past lend themselves to easy testing by someone without specialist knowledge and test equipment. Many analogue telephone lines are, however, presented on an analogue line NTE like the one shown above.

If your telephone lines are presented in this way, you should be able to test them yourself. You will need a working analogue telephone and a small screwdriver. By 'analogue telephone', we mean one that works on an ordinary phone line, like the line you probably have at home. If you are not sure, try plugging a phone into your broadband line. If it works there, it is suitable for these tests.

  1. Look for 1 or more analogue line NTEs labelled with the telephone number you are having problems with. There should be 1 NTE for each line you have on the number, so if you have 3 lines, there will be 3 NTEs.
  2. If there is a cable plugged into the NTE, unplug it, being careful to note which cable was in which NTE so you know where to put the cables back when you have finished.
  3. Remove the 2 small screws on the front, and remove the front section of the NTE. You will see another phone socket behind the front section of the NTE.
  4. Plug a phone into the socket and see if you have dial tone.

    • If you do get dial tone, try making a phone call, say to your mobile phone. If you can make a successful call, the line is working. If you cannot make a call, the line is faulty.
    • You can also try dialling 17070 (line on the BT network) or 174 (line on the Virgin Media network). On lines from most providers, this will result in an automated announcement of the telephone number associated with the line.
  5. Replace the front section of the NTE and plug the cable back in, if you removed one in step 2.
  6. Repeat steps 2-5 for the other lines.
  7. Any faulty lines should be reported to your line provider. When you report the fault, explain the tests you have carried out.
  8. If all the lines are working correctly, you might have a problem with your telephone system. Contact your telephone system maintainer for help. We can provide help with the products we support.



ISDN 2 is a means of providing telephone lines to a telephone system. Each NTE provides 2 lines, so if you have 4 lines, there will be 2 NTEs.

Generally, ISDN 2 is used for between 2 and 8 lines, with ISDN 30 used for between 8 and 30 lines. However, this is not always the case and it is possible to have more than 8 lines using ISDN 2.

You can find out if you have ISDN 2 lines by looking for the NTE (pictured above), which should be near your telephone system, and could be loose inside the data cabinet, if you have one, or mounted on the wall. There should be a cable between each NTE and your telephone system.

If some or all of your telephone lines are not working and they are ISDN 2 lines, carry out the following checks before reporting the problem to your line provider.

  1. Check the green light on the NTE.

    • If the light is off, this indicates a fault with the ISDN 2 connection. Report the fault to your line provider and tell them that the green light on the NTE is off. The fact that the light is off definitely indicates that this is a line fault no matter what BT or your line provider tell you.
    • If the light is flashing bright and dim rapidly, this indicates that the connection between the NTE and the BT telephone exchange is being initialised. If this continues for longer than a few seconds, report the fault to your line provider.
    • If the light is flashing bright and dim slowly, this indicates a problem with either the telephone system, or the cable between the NTE and the telephone system.

      1. Check the cable between the NTE and the telephone system. Make sure the plugs are pushed into the NTE and the telephone system properly. The plugs have a locking tab so it should not be possible to pull them out without pressing the locking tab to release it.
      2. If the cable is connected properly, it might be faulty. Try a different Cat 5 cable.
      3. If the cable is missing and you cannot locate the cable that should be connected to the NTE, call your telephone system maintainer for help.
    • If the light is on and the lines are still not working, this could indicate a problem with either the line or the telephone system.

      1. The light on some NTEs does not flash when the cable is unplugged. Unplug the cable and check that the light starts to flash bright and dim slowly. If the light does not start to flash, reconnect it and follow the steps above for checking the cable is connected properly.
      2. Report the fault to your line provider and ask them to test the lines and reset the ISDN 2 connection. Sometimes the test followed by a reset is enough to fix the problem. At this point, the line provider will tell you either that the test shows a problem or that the lines are testing OK. Note that the test is not perfect and sometimes lines that are faulty pass the line test.
      3. If the lines are still not working, call your telephone system maintainer for help. We can provide help with the products we support.


An ISDN 30 NTE (side view).

ISDN 30 provides between 8 and 30 lines, or multiples of 30 lines over a digital connection. ISDN 30 requires specialist knowledge and test equipment to diagnose and rectify faults. Please call us for further assistance.

SIP trunks

SIP trunks are not physical telephone lines as with analogue and ISDN, and instead route calls over the internet using VoIP (Voice over Internet Protocol). They are connected to your telephone system via either the same internet connection used for your computers, or a dedicated internet connection used just for your SIP trunks.

If you are having problems with your telephone lines and you know or suspect they are SIP trunks, the first thing to consider is whether you are also having problems accessing the internet from your computers. If you have SIP trunks that have either stopped working, or are working intermittently or with poor speech quality, and you are also having problems accessing the internet, the first thing to do is investigate your internet connection problems with your IT provider or internet service provider.

If the problem is with call quality, the problem might be that your internet connection is not up to the job. If calls start to break up (some customers describe this as sounding like the caller is underwater) when you are downloading, or uploading in particular, large amounts of data, it could be that your computers and telephone system share an internet connection and it might be better to have a separate dedicated internet connection for the SIP trunks.

Please call us for advice.

Hosted telephony

Hosted telephony, also called hosted VoIP, is a telephone system with the system itself hosted in a data centre somewhere with just the telephones in your office. Typically you pay a monthly fee per telephone. The telephones connect over the internet and are therefore subject to the same possible problems as SIP trunks, above. If you are having problems with your hosted VoIP telephones, follow the advice given above for SIP trunks.

If you can't resolve the problem or need more help, please call us for advice.

Call us on 0115 938 9685 or use our contact form.