I have just gone from ADSL to VDSL, and am using a BT modem connected to the WAN2.

I am only achieving a throughput of 1.5M

If I use the ISP supplied technicolor router, I obtain the full 78M.

Why is the Draytek only allowing 1.5M through the WAN2?

I have updated to the latest firmware.

Any ideas?

QOS is disabled.

Thanks.

Have connected to the correct wan giga incoming port?
have you enabled wan>general set up wan 2? then you may need add the vlan tag value with 101 of bt 's infinity
There you may try the Physical Type from auto navigation to 100 half dublex
it is also good idea to disable wan 1
try change cables, if will make difference

Had another 2830 from another site going spare, so have just factory restarted it, and then connected that. I get 74Mb from that. If I then download and upload the config from my current 2830, the new one has the same issue, so must be a config issue - I am going to have a play and see if I can see it before starting from scratch!

Didn't realise Infinity needed a Vlan tag, it seems to work without with the standard config settings.

before you start all settings from the scratch update the firmware to 3.6.7 using the rst file to clean previous firmware conflicts.RST is suggested for this reason
Your report may helps others had same issue, was somewhere in here same issue, will spot it later will help someone else