You can check the Xfinity web site but I am pretty sure you can not buy a modem from Comcast. You would need to buy a compatible modem from a third party retailer and whatever warranty comes with that particular brand would apply. Odds are good you can get one cheaper than the monthly rental fee charged by Xfinity that would add up over time but you will need to make sure to keep up with the periodic firmware updates.
I am sure that if it is in its warranty period that yes it will.. if not, maybe not. Make sure to put a good surge protector or UPS on your modem and router so that power surges do not harm it since it is plugged in and powered on all the time.
I agree with both Webb & Steve.
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