Home warranties tend to cover the bare minimum required to repair items that break. They won't cover elective renovations.
@Kristi July I agree with comment above - they only cover what breaks. And only per the specifics of the policy, which differs per state I believe. I have a policy with American Home Shield and you can view the coverage online even if you don't have one...so take a look, it will answer many questions. Search 'American Home Shield.' Best of luck!
This is a little out of date, but 20 years ago when we bought our home we had a policy with American Home Shield. Our heater went out in December. They kept telling their repairman to make small changes. Nothing worked. We were without heat for 3 weeks. One day I came home from work, and a neighbor told me that the repairmen had been on the roof, working on the unit again. I didn't know they were coming out. Since they had been out, we tried the unit that night, and it caught on fire. Not a big fire, just contained within the HVAC. The next day the repairman came out, and called AHS to tell them all the parts that had burned, WITHOUT EVEN GOING ON THE ROOF TO INSPECT THE UNIT!! AHS finally agreed to put in a new HVAC. It took a fire to convince them that the HVAC was not worthy of repair. I've never trusted AHS, or that repairman since.