Noisy Telephone line testing


Noisy or crackly Telephone line testing

This Testing method if completed correctly can help you locate the problem with your Telephone Line

BT Engineer man on telephone

Listening for a crackle !!!

This test is not the most scientific, and relies on the sensitivity of the human ear, but it works great.

Learn about some simpleTelephone  engineer tests you can perform on your telephone line.

Before I go any further I need to point out that this test is for British Telecom (BT) analogue phone lines in the UK only. There are likely similar test services out there for other services.

Testing from the local exchange to your building.

In order to rule out interference from inside the building it is important you test at the Master telephone Socket. This socket is where the copper pair from the street enters your house. You can remove the front panel from the master socket which will disconnect all extensions in your house and reveal a single phone socket. This phone socket is a direct connection to your street.

Connect a good telephone into your master socket and dial 17070.

If the number doesn’t work for you and all you get is ”There is no CLI detected for this circuit”.

This means you have Caller ID blocked on your line. To get around this dial  1470 17070 instead.

You should hear a female pre-recorded voice say:

This circuit is defined as 01234 123123.
BT line test facilities.
Please press 1 for ring back, 2 for quiet line, 3 for fast test, 4 for fast cleanse or clear down.
[message repeats 3 times]

Select option 2 (quiet line) and listen to what you hear. You should hear perfect silence on the line – there should be no pops, clicks, whistles, buzzing and the like.

If you do not hear silence first check it isn’t the phone you are using, wiggle the cable a bit to see if that affects it, if not then you know you have a problem with your line to the BT exchange.

Any problems with ADSL connectivity (low speed, connections always dropping, etc) are likely caused by this.

You can now put your master socket together again and re-enable all the phones in your house.

Testing the internal wiring of your building.

So you’ve performed the test at the master telephone socket and all sounds good.

Now you can perform the exact same test again, but this time with a telephone where your ADSL modem would connect in. This should include any and all telephone extensions you intend to use.

If you hear noise on the line now you can deduce that the interference is coming from inside your house.

Things to check for are telephone cables running near transformers or motors and compressors, faulty equipment on the line introducing noise. Hopefully by removing equipment and tracing back the line you will be able to identify the source of the noise and replace/remove it.

If this works for you and you have fixed your telephone line then CONGRATULATIONS!!!


If all else fails give me a ring and I’ll be happy to help

01277 287077 – 07882691192