I don't know about warranties, but you need to fix the leak ASAP. Mold
can be a worse heath issue than water damage. Make sure you spray the
inside of the wall with bleach or a mold inhibitor after you fix the
leak. Is the leak on the straight section of the pipe or on the solder
joint? You need to cut out a section of the wall and see exactly how
bad the leak is so you can fix it.

Ace hardware has a clamp for about $7 for a leak on the straight
section of copper pipe. That has worked for me in the past. I used a
Instaclamp (instaclamp.com) on my 1/2' solder joint leak and fixed the
leak in 5 minutes. The $25.00 it cost me beat the cost of a plumber or
me having to solder it.

Hope this helps,

Sozoman