Commercial espresso machines are normally NSF & UL approved for the US market. The machines come in two main categories, traditional and super automatics.
They are then divided between heat exchanger and multi boiler and then one or two step Super Automatic.
Heat exchanger machines normally have 1 point of temperature reference for controlling the steam and espresso water temperature via a pressure stat in the boiler normally providing a 3 degree swing up & down in temperature. Some machines do have the ability to have cold water and hot water mixed at the brew group for modifying the brew water temperature to a limited degree. They are generally used in the average food service operation where cappuccino is served in 6 to 8 oz. cups and were water temperature is not a critical factor to serving consistent espresso. There are heat exchanger machines that have a more sensitive pressure stat of 2 degree swing up or down and offer higher power rating to help maintain improved water temperature stability for busy up scale restaurants or coffee shops.
Independent boiler machines are normally used where cappuccino is served in larger to go cups of 12 to 22 oz. and espresso water temperature is a critical factor in achieving a more consistent tasting espresso coffee or when using 2 different coffees that may require different temperatures for getting the best taste. . the water temperature is controlled through a PID temperature controlled thermostat with in 1 to 1/2 degree.