Q:

DSL upload link breaks down. Where to look and not to look?

In a small office where I set up the network, we recently started to experience WAN problems on the (V)DSL line. Specifically, up to three times per day the upload link breaks down to almost zero resulting in problems with any activities needing upload bandwith (e.g. sending email attachments). A simple reboot of the DSL modem suffices to solve the problem, the upload link immediately comes back again.
The telco technician came to check the connections and stated that there are quality issues with the house connection line. Literally, he said something about 1200 FEC and 300 CRC errors in 10 minutes of measuring (not that these numbers would mean much to me). 
The internet provider will send me a replacement for the modem just to rule it out as an error source. I think that's prudent, after all we did not have any connection issues in more than 10 years. On the other hand, the modem we have is only two years old and also never showed any problems until two weeks ago when this started. 
Now to my actual question: about 4 weeks ago, i.e. 2 weeks before we started experiencing the described issues, I replaced the Firewall that does the pppoe dialing. 
Considering that a reboot of the DSL modem (router in bridge mode) solves the issue each time, is it theoretically possible that the Firewall behind the modem is somehow responsible for the break down of the upload link?

A:

It is highly unlikely that the firewall is to blame. The most likely cause is the wiring as the technician explained. You should hire a cable installer to replace or repair the bad wiring, test, give you the test results, and guarantee his work.

