I have a TalkTalk ADSL service and in November 2017 I had a fault where I would lose sync both randomly and when the phone was picked up or rung. There was also data noise audible on the phone when the router was connected. I assumed this was a high resistance fault on the line, and indeed the remote fast tests did sometimes (but not always) state the presence of a CIDT fault. However after 1 PSTN and 2 SFI Openreach engineer visits the fault was found to be with the port on TalkTalk’s MSAN in the exchange. I was changed to a different port and all was well.
However in April 2018, after my router had been in sync for 160 days, the same symptoms reoccurred. A fault was reported and I gave the attending PSTN engineer the name of the SFI engineer who ultimately found the fault last time. The SFI engineer told the PSTN engineer what to test for, and it was once again found to be the MSAN port. Once again this was changed and all is now well.
The engineer said it is very rare for a port to go bad, so two going bad suggests something else is causing it, perhaps some other undetectable fault on the line. The engineer left and returned to his van, and I reconnected my internal wiring and router (I had been using the TalkTalk provided HG633 router and a basic corded phone plugged into the test socket via a dangly filter for diagnostic purposes, but my normal set-up has a data extension from a MK3 SSFP and a TP-Link VR600 router).
From the van the engineer initiated a line test (presumably this is standard procedure when closing a job) and got back a CIDT fault. He tried this 5 times and got the same result, so returned to the house and asked me to remove everything again. On initiating a final line test, no fault was found so he closed the job, but commented that perhaps the house wiring and/or the VR600 is bad and is causing the MSAN ports to go bad.
The line seems perfectly stable now, and I did try swapping to a different pair on the data extension which made no difference to anything. But this has got me wondering, can bad wiring / the VR600 in the house cause MSAN ports to go bad over time (excluding things like shoving 240V down the phone line which would presumably blow up the MSAN port in an instant)?