I’ve tried to Google “bintec” router but I don’t find a good manual in English. Besides, I’m not an expert on hardware firewalls. I think the update is done by http traffic on port 80, no I won’t expect that you should ‘open’ a port into the hardware firewall… it should be already opened…
Please, post the last 200-250 lines of avast log: C:\Program Files\Alwil Software\Avast4\DATA\log\Setup.log