Let me get this straight, you plugged the fax directly into voice port #2 correct? (No wall jack involved) and all is good when tested with butt set. Voice port 1 on the ARRis TM 402 has both line 1 + 2 on it . Voice port 2 should be line 2 only. I would plug fax directly into voice port 2 with nothing plugged into port 1 and see what happens. You are aware that HP all in one Fax /scanners will NOT work with this unit. I spent hours . Also beware there are some fax's that will SHORT the unused pair internally so avoid using both pairs with the silver satin phone wire. THis came directly from an Arris engineer I emailed. Oh if you work for Comcast they don't pay you for the 2nd line its included in the price