In reply to a post by MHC:

The problem with errors though is continuous apart from the 3,5 hours every evening. That points away from heating - who leaves heating and hot water on 24 hours/day?

The two questions are: what is causing the errors? And what is suppressing them in the evening? which will the lead to: is it the device being turned off? or going into active mode? or another close-by device having a filter on the power lines which is absorbing e interference?

What happens to the noise margin when the error rates rise and fall?

Stays the same.

If errors are caused by noise I would expect the SNR(M actually) to fall while they are occurring, and rise when they stop.

Which suggests to me something else is going on in the router causing it to screw up in some way . Is there any sort of timed backup takes place? Or remote scan of a computer on the LAN?

I don't think so. It's a Billion 8800nl and I factory reset it on Monday as I wanted a fresh start with BT. I will take another look now though.

Checked router and can't see anything. I have uploaded images of my graphs for FEC, SNR andBitSwaps for the last 24hrs so you can see what's happening. They are here.

And looking on MyDSLWebStats at your SNRM/band - they are consistent at 6dB with the expected short burst of noise or interference. There is nothing matching the evening FEC rate change.

I've managed to ship the wife off for a few hrs with the kids now so I'm in the process of turning everything off to see what happens!!

Looks as though you were unsuccessful in your hunt! And that the 19:00 change has also occurred again!

Cancelled engineer visit yesterday but OR turned up today anyway! I happened to pop home from work to get a fibre patch cable and van was outside. The guy said it wasn't chargeable job but that he hadn't found anything wrong. Back to the drawing board I guess.

One thing I did notice though is that the noise disappeared early yesterday - at 16:34 instead of 19:00. As yesterday was a very warm day, this says to me that it may not be somebody's heating coming on. Doesn't help much but least it's one thing probably ruled out.

I saw that ... although the noise did come back for a short period fro around 18:40 to the usual 19:00.

I presume all your tests at home have show nothing ...