Another weird speed problem

[#1]

My line had been stable for a very long time with a sync speed of around 2.8M @ 6dB.  The line would always remain up for weeks on end with no issues.  Then suddenly the sync rate slowed (no line drop) to 1.8M @ 15dB.  When I rebooted the router I only get 2.2M @ 12dB.  Why would BTw raise my SNR margin like this?
Now my Internet connection is virtually unusable and it has to serve a large household.  Iplayer is completely unusable.  youtube buffers for 30s then plays 1s, then buffers for 30s, etc etc... Even small web pages take forever to load.
I had a similar issue a few years ago and it took years for speeds to recover.  I am still on ASDL1 BTW.
BT speedtest shows download speed of 1.3M with an IP profile of 1500Kbps but the connection "feels" like dial-up.  Exchange status shows green.

[#2]

If possible connect the router to the TEST socket within the BT master socket if you have that type, then get the router line stats and the data from the BT Performance Test
Kitz, how to get [color=red]line stats
The BT PT

[#3]

HI mapletree,
If you can let me know if/when you can plug it into the test socket then I can run some checks for you. The SNR will have gone up to 12dB as a reaction to some interference. This could be caused by internal wiring or something external. The test socket will help us eliminate the internal wiring as a cause. Also, the sync rate won't slow, there will have been a drop, but that can be short and easy not to notice.
Jojo

[#4]

Thanks, Jo.
The router is plugged directly into a filtered faceplate in the NTE5 master socket.  Apart from one phone there is nothing else connected and no other internal extensions.  I am not at home right now so can't change anything but I don't think there is anything wrong with my wiring.
FWIW my router reports DSL uptime and, after the slowdown but before I rebooted it, it was showing 812 hours uptime.  It doesn't usually get this wrong.
I still don't think it explains the 12dB SNR target margin as I thought this should only go up after many problems and only in 3dB steps.
I had a similar issue a year or two ago when the line would drop once only and the margin would be up from 6 to 12dB.  Back then I used to monitor the connection 24/7 so I could see there were no other problems.  I had stopped doing this recently since I hadn't experienced any issues for a while -- typical 
I don't get very good speed at the best of times so this is a major blow.

[#5]

It could be the filtered faceplate. Can you take it off and use a normal filter? I could reset the SNR but if there's a problem it'll just go back up or make it even worse. I'd feel much happier doing it from the test socket.

[#6]

I can dig out a filter from somewhere.  When can you do the tests?  BTW Line is stable for last 24 hours but connection speed is lower than it used to be @12dB.

[#7]

Hi mapletree,
have you been able to do that?
Jojo

[#8]

Yes.  Router is plugged into the test socket. 

[#9]

Thanks, I'm going to reset the SNR and see what happens. Ill check it a bit later for you

[#10]

Thanks, Jo.  Will this start a new 10 day training/stabilisation period too or is it just the margin that is reset?

[#11]

It'll restart the training period, though if it's 21CN it should be over in a bit less than 10 days with any luck.

[#12]

HI mapletree,
That seems to have worked. I've just raised your profile to 2500, so you should see that shortly.
Jojo

[#13]

Great, thanks.  Let's hope it lasts    Is it on 21CN BTW?

[#14]

I'm afraid not, it's 20CN ADSL Max at the moment.

[#15]

I don't mind    AFAIK speeds might be worse on ADSL2.