Intermittent Broadband Faults

Intermittent faults can be frustrating for both the end user and ourselves from a support perspective. Rarely is there a simple "make this line stable again" fix, and some of the changes we can make can have implications to the speed achieved.


Normally there is a logical reason for intermittent connections, and why a stable line rapidly goes down hill. Here is a list of some of the common causes:

  • Noisy phone line (raise to line provider as voice affecting)
  • Faulty filter (they're cheap, try another)
  • Faulty router (we understand that not everyone has a spare, but if you can rule it out, it's cheaper than an engineer visit to tell you the router is faulty)
  • Faulty or damaged cable to the router
  • Long extension cables
  • Operating router from a slave socket
  • Router recently moved next to radiator and overheating
  • New electrical cables run next to the phone cables (electrical interference)
  • Weather related intermittence (external to premises)
  • Sky TV boxes not sitting behind filter
  • Other equipment on the same line interfering


Some of the more unusual reasons we have seen include:

  • Street light interference
  • Farmers electric fence
  • Christmas tree lights
  • Electrical interference from pylons


Given the wide range of possible scenarios the easiest way to diagnose is the logically rule out internal issues before we raise this further. The chances are that an engineer appointment will need to be booked with an intermittent fault. So as long as we can rule out any equipment up to to the master phone socket, we can be confident the fault must be external and beyond what a customer is expected to be responsible for.


When raising a fault these are the things we would like to see:

1.Has all non-ADSL equipment been removed from the line? This is a good first step to ensure that what you're dealing with is either the broadband or the phone line, not third party equipment.

2.Confirmation that you have replaced the filter, cable and router. BE HONEST. Stipulate exactly what you have changed so that we are informed and we don't have to ask. Mention any makes and models used they always ask us.

3.Check the line for noise and interference. This is to ensure that we're not dealing with a noisy phone line. A noisy phone line for voice calls will cause intermittent issues for broadband. The line needs to be free from interference for broadband to stand any chance or working. To test plug a handset into the filter and dial 17070. Listen to the number announced and choose option 2. This is the quiet line test. You can listen for crackles, pops, or static noise. If present, don't raise this as a broadband fault, deal with it as a noisy line with the line provider. When dealing with a line provider be careful to stipulate that this is a quality issue for the line. You can mention that broadband is also affected, but be sure to put the emphasis on the voice quality. Fix a noisy line issue you the chances are you'll fix intermittence on the broadband.

4.Confirm that the router is connected to the master socket and is free from any electrical interference. As per some of the examples above, lots of issues have been the result of electrical interference which is sometimes referred to as REIN (Repetitive Electrical Impulse Noise). Simply ensuring that no electrical cables or products are near to the phone socket or cables should be enough.

5.Are there any patterns to the intermittence? We would like to know if there are time of day related issues. If the evening is worse, is it because the phone is also in use, or is it because the TV is on and the router sits next to it. Both scenarios can effect the quality and reliability of the connection. Make use of the session history page within the control panel. It shows you the length of sessions and the disconnection cause. Make use of the glossary tab on this page if you are unsure what the disconnection causes mean.

6.How often are the disconnections occurring? A customers definition of intermittence can inevitably differ from our suppliers opinion. For BT Wholesale and C&W to take intermittent issues seriously we need to see at least a few disconnections every hour, if not more frequent. Disconnections occurring every couple of hours, or a couple of times a day, although annoying, are not going to be classed as intermittent. If we end up having to arrange an engineer visit, and the engineer can't see this happening, or their diagnostics fail to see a random drop, they will simply walk away stating "right when tested" and the visit becomes chargeable.