Well after running for a week nothing had changed. So last night I changed the router to the old DG834GT. Connection speed increased, noise margin(down) dropped and Line Attenuation(down) dropped.

ADSL line is on Fastpath and has been all the time.
Connection Speed 4960Kbps(Down) 448Kbps(Up)
Line Attenuation 11.0db(Down) 5.5db(Up)
Noise Margin around 14.0-15.0db (Down) 24.0db(Up)

Only thing now is Noise Margin is constantly jumping, DG834GT Graph, compared to the previous router, DG834N Graph.
So is this acceptable or should I put my other router back on?

Suppose I should give my setup. Phoneline comes into house through wall and terminates at master socket where it comes through. Filter fitted to master socket, ADSL cable goes to Router, 5m of foil shielded RJ11 to RJ11 cable. Another filter fitted to phone outlet of filter, then a two socket adapter fitted to this phone outlet, one cable going to phone and the other to a AIO printer.
I did try a double phone and modem adapter with surge protection, in the master socket, and done away with the filter on the ADSL line and a filter in each of the phone outlets, but this increased the Noise Margin marginally.

Have sent a request to Demon to try and get the Noise Margin reset. But awaiting a reply.

Thanks

In reply to a post by Scottish_Pete:

Well after running for a week nothing had changed. So last night I changed the router to the old DG834GT. Connection speed increased, noise margin(down) dropped and Line Attenuation(down) dropped.

ADSL line is on Fastpath and has been all the time.
Connection Speed 4960Kbps(Down) 448Kbps(Up)
Line Attenuation 11.0db(Down) 5.5db(Up)
Noise Margin around 14.0-15.0db (Down) 24.0db(Up)

Only thing now is Noise Margin is constantly jumping, DG834GT Graph, compared to the previous router, DG834N Graph.
So is this acceptable or should I put my other router back on?

Suppose I should give my setup. Phoneline comes into house through wall and terminates at master socket where it comes through. Filter fitted to master socket, ADSL cable goes to Router, 5m of foil shielded RJ11 to RJ11 cable. Another filter fitted to phone outlet of filter, then a two socket adapter fitted to this phone outlet, one cable going to phone and the other to a AIO printer.
I did try a double phone and modem adapter with surge protection, in the master socket, and done away with the filter on the ADSL line and a filter in each of the phone outlets, but this increased the Noise Margin marginally.

Have sent a request to Demon to try and get the Noise Margin reset. But awaiting a reply.

Thanks

Are there no LLU providers in your exchange ?samknows checker will tell you if you don't know already.
If there is any llu such as be/02 i personally would not be having a upto 8mbit ip stream service, with such a short line you should get around 22mbit maybe more, never mind an upto adsl max product that is subject to bt DLM the downstream sync appears to be Capped at 4800 why i don't know that would also account for the high snr which has been deliberately raised to effectively cap the connection Demon are the ones to be asking,
it sounds as if there is some type of fault that affects your line attenuation but i would doubt that it will lie between your master socket and exchange could be the equipment at the exchange failing,

Unfortunately on a market 1 exchange, so stuck with BT Wholesale and any upgrade will be in the dark and distant future.

Thanks,

I found that the DG834GT always gave me a jumpy graph.
My best move was to get the old style BT office hub.
Made my line jump from 2.something connection to 5 something connection
I live in the sticks outside of Kilmarnock and the BT engineer was surprised to see that the hub had now gave me a 5mbps profile

I loved my DG834GT - it was a lovely router, and was only *replaced when I was able to start getting faster speeds that needed a draft-n router.
The router was easily tweaked, and was good fun to use.
Ok, GT had to be replaced due to becoming faulty [under warranty]. I sold the sealed/un-opened replacement on Amazon.

Only a pity that it couldn't go fasssterer.