Circulating Hot water system

I have just moved into a new home with a circulating hot water system. My problem is that the water does not get quite hot enough. This, inspite of the water heaters being set at near the upper limits of the heat control. The house is long, 86 feet, and has four and one half baths, and the usual hot water needs at the kitchen, utility room, etc. What could cause this problem? Volume of water is ver adequate.