Two HD Cable Boxes, Only one works! - XFinity

I recently had Comcast send me an additional box for the bedroom, after only having one TV downstairs. The two-way coax splitter installed for my system only has room for the downstairs Cable box and the internet modem. So rather than deal with waiting for a service appointment, I purchased a splitter to accomodate the upstairs Box. The splitter says its rated for HD/Broadband cable coax systems. Long story short - Only one box at a time will work. When I have the two boxes and the modem plugged into the coax splitter, only one box will recieve signal. If I unplug one coax to one of the TVs, the one that doesnt work will instantly recieve a signal and work properly.

Am I missing hardware here? Why wont both cable boxes work simultaniously off of a properly rated coax splitter?

This question, "Two HD Cable Boxes, Only one works!," is about XFinity-Comcast TV television equipment.

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