I have probably bought and installed for several clinets about 20 Vigors (models 2830 and 2860 mostly).
I am aware of the notorious reboot problems that some models may have but one way or another I have managed to find solutions.

In May I bought a Vigor 2925 for a growing company. There is dual wan (adsl & vdsl), 16 Pcs and 2 servers and about 5-6 ipsec vpn tunnels for partners.
The 2925 reboots by it self randomly, It may reboot twice a day, once a day, once in a week or once in fortnight. The max uptime has been 16 days.

I have simple configuration, the Lan for the PCs and one VLAN for the TPlink access point. UPnP is not enabled and i don;t have synology or plex/sonos clients-servers in network (I have read in other posts that these may cause reboots)

I have contacted support and provided them remote access, syslogs and screenshots but nothing strange is in there.
I have tried changing the psu but no luck. I have tried placing a network switch between the modems and the wan ports but no joy either.
I have borrowed another 2925 and used with my configuration but that also reboots. I have tried disabling the VLAN but still reboots. I have tried disabling the DDOS and the hardware acceleration but still reboots. I have tried resetting to defaults with the reset switch and also re-applying the firmware with the .rst and manually reconfigured but still reboots. I was given a September 2014 beta firmware but still reboots.
I have also tried moving the psu from the UPS to a normal power outlet but still reboots.

Now i am a bit desperate, remote vpn partners are complaining when disconnected, staff calling me all the times and boss is asking what can be done.
It is enquiring about the possibility of changing to Zywall series but I really would like to hear from you guys what other possible clues as to what is causing these reboots.

I would also like to hear from othe 2925 owners if they have any reboot problems with their units.
Thanks in advance

Hi, i am not owner but i have suggestion to try, maybe each step a time

wan>general setup>details page use the correct MTU from each isp (wan 1 & wan 2)
Lan> general set up > details page > DNS Server IP Address, add your own one, example google ones or opendns (that will work for both adsl & vdsl)

If still issues & you have wireless, disable to see if there is still problem
Disable & ipv6

Hello babis.
The MTU value is 1492 for both isp.
I am already using opendns servers as i have account with them.
It is not the wireless model and ipv6 is already disabled.
Thanks for the reply.

As last attempt i would say to roll back firmwares from the link (assuming you have the latest, try the other 3) you may be lucky one of them to be more stable for your issue, perhaps use of rst file is better for a clean install
ftp://ftp.draytek.com/Vigor2925/Firmware/

I would like to update the thread by saying that I finally solved the reboot problem. The cause was the UPS. I changed to an Eaton true sinewave model and no reboots from then.
Funny thing though, the previous UPS also powered a couple of procurve switches and 2 bridge modems and another router which none had the reboot symptoms.
Well, that's the IT world!!