FTTC speed problem after modem replacement

Last weekend we had the chap come to swap out the BT modem on our fibre. Fibre is with Zen internet.

Prior to this, we were getting ~32 meg out of it, according to the thinkbroadband and several other speed testers.

After he went, it had dropped immediately (10 mins after he left) to 18 meg. "OK," we thought, "it needs a little think."

But a week passed and it's no better. We spoke to Zen yesterday about it. They got us to run the BT speed tester, which reports 36 meg. I'm not sure exactly what that tests or how. Anyway, we're still only getting 18 meg as far as we can tell, from 4 testers on various continents, and from the reported speed of files being downloaded. It is noticeably slower than before, when we used to download a 30-min podcast in ~30 seconds, and now it's ~50.

Zen also took the Netgear router out of the equation by connecting us briefly directly to that BT modem. Still 18 meg. At this point they told us that since the BT checker reports 36, BT won't touch it or see it as a fault. Game over, although they've turned on the ping response in our router to watch it for a couple of days.

Taking matters into our own hands, we've also swapped the wall-to-BT-modem cable with one from next door's house (no change). We took our new BT modem to a friend's house (who gets ~34 meg out of his) and tried it there, and his speed was unchanged so it's not the modem either. We get about another 0.5 meg out of it if we unplug the phone from the same socket, but that's all. There's no internal phone wiring in the house from that socket, and we're not using wireless off of it either. Just wall-master socket-modem-router-single PC, ethernet-wired. It's no different if we have the rest of the house network plugged in, to be fair.

As far as I can tell, this leaves either a fault in the master socket, or something occurred when that modem was swapped which has got something stuck somewhere along the line. As I pointed out to Zen, it's a huge coincidence that this happened immediately after the engineer came.

If anyone has any ideas of anything else to try, or something to tell Zen to do, we would be most grateful. BT fault or not, it seems obvious to me that with 36 meg being "delivered" but only 18 meg being "useable", something somewhere is blocking 50% of our bandwidth.

Open to suggestions!

Post a screenshot of the result from the BT java speedtest.

I presume this is the one at speedtester.bt.com?

Interestingly, I ran it and it said 16 meg the first time!! Then I ran it again immediately and it said 36 meg.

First and second ones

Then I remembered that it doesn't like Chrome very much (doesn't give the little graph thing) so 3rd one is 3 mins later again, on IE.

3rd one

So that's the 3 replies in the space of 5 minutes tops. The first one is particularly interesting since that's the first time we've seen it say anything other than 30+

If that's not the test you want, could you point me to it please?

IP profile for your line is - 38.71 Mbps

This means there is nothing wrong with your connection. I guess Zen is capping your speed.

Hmm, I imagine that's by accident and not on purpose, otherwise the tech guy yesterday would have mentioned it.

Or not...

But they don't have (or say they don't have) any capping, shaping or whatever.

Weirder and weirder...

We've also just been and kidnapped our friend's entire BT modem and cables and just tried that as well. No change there either.

Congestion on WBC link maybe.

Do speeds improve at the quieter times e.g. breakfast 7 am to 9am

Alas not, we've tried at all hours, morning, midday, evening, middle of the night even. Always around the same mark.

Zen's service details on their site swear blind they don't cap speeds or traffic shape in any way.

Don't know what to say to them next, really.

Which PSU is being used by you and your friend? The old black one or the new white one?

This could be a complete red herring, but the new modem claims to need 1A supply, which the white one is rated at. The old PSU is rated at 0.6A and the old modem was 0.7A requirement.

BT appparently, and some good figures from a couple of posters, say the black one should cope. But it is worthwhile ruling out the possibility here that it can affect the throughput.

We both have the black ones with 0.6 written on them. We've tried both, and both in different mains sockets.

I suppose that could mean that our modem just doesn't like the 0.6 but his one does... we don't have a white one to try. When the neighbours come home, we'll see what colour theirs is and try to nick it if it's white

We've used his PSU on his modem on our line, and his PSU on our modem on our line. Neither made any change.