Had issue with furnace for two seasons; various companies didn't resolve it. I went in to National, explained issue, appt made for Ernie, the service manager to come out. Thank God for National. Ernie, told me the problem, told me the furnace was still under warranty for parts. Once Ernie returned with parts, it was fixed in five minutes! I was so grateful since it was too cold to stay at my home. Five star customer service in the office and field. I fully recommend National.