I've just logged my second fault with Zen since I signed up in Feb 2012.
Early yesterday morning ( Sep 28th ) my broadband resynced and it's been doing so on and off ever since. Lots of errors are being logged using DSLstats. Previously we had 4086 FEC errors per hour and now we have over quarter of a million.
Our target SNR was until quite recently 6dB but a couple of weeks ago it was set to 3dB and we saw a decent sync speed increase from about 67Mb/s to to 76Mb/s. We now have a downstream SNR of 10dB, sync of 45Mb/s down ( was 76) and 6Mb/s up (was 20). We are also now experiencing quite frequent dropouts and stuttering - Radio Four from TuneIn via Alexia is a pain now.
Thankfully (!) the analogue voice circuit is noisy as hell and so I've logged a voice fault with Zen CS. I was asked to do all the standard master socket tests and use a different analogue handset and a filter in the master socket. As we have a DECT phone system the only analogue phone connection is the flylead to the DECT base station.
Zen have just called back to confirm an engineer Openreach will check the line on Monday morning ( 8am to 1pm) and possibly need access to the internal wiring - all 6 inches of it!