When diagnosing your reported internet issue, you may hear the term CPE checks.
This stands for Customer Premises Equipment; which is essentially everything internally from the BT master socket.
In the event that no fault can be found with your broadband service, BT requires that the following items are checked before progressing any fault:
1) Check the router in question; depending on the age of the router this could affect speeds or intermittent connectivity due to banding.
2) check the filter; the filter could be damaged due to electrical surges, or by simply being fragile and could already be partially damaged. It is advisable that you change these
3) Change the router for another router; remove the current router that you are using and swap it for another router. This router can be borrowed from anyone, it just needs to be borrowed whilst tests are going on. The router in question doesn't have to be fully configured, you just need to lash it in.
4) Remove non-xDSL equipment: any other equipment on the line can have a detrimental effect on the performance and stability of the line due to noise and/or interference. Fax Machines, TV Boxes and additional phones can cause a problem. Disconnecting them will remove any noise they generate from the line.
5) Connect to the master socket: internal extension wiring can either pick up interference, be damaged or could even be wired incorrectly. As such connecting to the master socket should eliminate some of these issues.
6) Carry out a 'quiet line test'; plug the analogue phone into the master socket and dial 17070: if a popping/crackling sound is apparent, this needs reporting to PSTN provider and they will do more tests to see what the fault is