New line VERY slow against estimated line speed, HELP Please.

[#1]

I visited one of my referrals in their new abode and they told me that their broadband speeds are dreadful compared to their last place. According to their plusnet account the speed estimate for the current line is 3Mbps however the current line speed is set to 250. Although the Netgear router itself shows downstream sync of around 620.
Now I have a fairly good idea why this might have happened. They have their router at the top of the house connected to the only BT socket at the bottom of the house via what appears to be a 15 metre extension cable. Is this likely to be the culprit?
I plan to take a wireless adapter around, move the router to the master socket at the bottom of the house and  test if they can connect to it wirelessly from the top of the house. If that works ok then get them to buy their own adapter.
So the router will probably move temporarily for the test then permanently after they get wireless adapter kit. What process do I need to go through to get the line speed to re-train or is this automatic and how long will it take?
Cheers
Peter

[#2]

The extension cable is very likely to the problem, something is causing much lower syncs. As it's a Netgear I'd suggest installing RouterStats to keep an eye on the sync speed and noise margin.
With the router installed where it is go to the stats page and then try ringing their phone number to see if that affects the stats.
I presume that they have a doubler in the master socket, the extension with a filter at the top of the house in to which the router is plugged. Do they have a phone or anything else plugged in at the bottom of the house and if so is it filtered as well?

[#3]

Hi Peter,
Mind PMing me with the referrals username so I can run a couple of quick checks on their telephone line?

[#4]

They have a doubler at the bottom. One line has the filter and the wireless phone base station, the other (unfiltered) goes straight to the top of the house to the router. There are no other phones connected to the system.

[#5]

Quote from: Jameseh

Hi Peter, Mind PMing me with the referrals username so I can run a couple of quick checks on their telephone line?

Will do James, Cheers.

[#6]

Quote from: God

the other (unfiltered) goes straight to the top of the house to the router.

Where there's another filter I hope!

[#7]

Thanks Peter.
As I mentioned, you'll need to eliminate the internal wiring issues.  It doesn't look that bad from the line tests though.

[#8]

Oh dear,  have I been doing this wrong for years? I thought you only filtered cables that had phones attached, there is only the one phone and that is filtered. I didn't delve behind the desk to see what the router was connected to but I quess it must be an adapter or a filter, dut deffo not a telephone as well.

[#9]

I'm guessing that behind the desk is a filter because of the different plugs used - but you do need to check!
Comparing the stats when the router is upstairs and when it's directly in to the master socket is a must.
<enormous understatement warning>Some extension leads are not very good.</enormous understatement warning>

[#10]

@God: If you have a long extension cable it may affect your speed.  However, with a good quality TP cable, you may not notice any drop in speed.  The best way is to have the router next to the master socket and run an ethernet cable back to your PC.
@jelv: Why would he want a filter for the router?  I thought all routers have inbuilt filters.

[#11]

When I went over and checked the router again it had re- synced to around 3k, I rebooted it a couple of times and found it went up to just over 4k. I moved it to the master socket and found the sync speed was the same so it has been moved back to the top. Mysteriously the speed has improved dramatically since my first posting!

[#12]

I have used a XTE-2005 box which vastly improved my connection, this filters the signal at the box with a high quality built in filter. A lot of the free filters the come with the modem are rubbish.
This should be fitted by BT though as it replaces their box which you should not touch, there are though lots of instructions on how they would do it if you paid them  
I've also been looking at the i-plate, this is legal to fit as it just plugs into the one you have. Have a search fot it theirs plenty about roughly about £5ish quid, they do require filters so again look for better quality ones.