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Single Boilers

How Single Boiler Espresso Machines Work

Single Boiler Espresso Machine Diagram

  • Boiler fills about half full with water
  • The machine warms up, stabilizing temperature in the boiler and the group head. Depending on the machine/settings, the temperature at the brew group will be somewhere between 198 degrees and 204 degrees.
  • If the machine has a PID, the brew temperature can be adjusted and maintained accurately
  • When shot is pulled, water is pulled directly from the boiler. Temperature remains stable (how stable depends on the machine)
  • After shot is completed, the machine can be switched to steaming mode. Before steaming can take place, the boiler temperature has to increase to provide enough steam pressure for frothing milk. At about 255 degrees, the machine is ready for steaming.
  • On most machines, the increase in temperature for steaming indirectly raises the temperature of the grouphead.
  • After steaming is completed, the steam functionality on the machine can be switched off, allowing the machine to cool back down to brew temperature.
  • While the temperature can be pretty stable for brewing the first shot, the temperature for any additional shots won’t be as stable due to the increase and decrease of temperature for steaming. This creates flavor flaws in the espresso.

Advantages & Disadvantages of Single Boiler Espresso Machines


  • Simple design
  • Faster warm up time
  • Ability to adjust brew/steam temperature independently
  • No cooling flush (some still may require temperature surfing)


  • Wait time between brewing and steaming
  • Less temperature stability
  • In general, smaller boilers with less steam pressure

Is A Single Boiler The Right Kind of Machine For You?

A single boiler is a good machine to get if you primarily drink plain espresso and only a limited number of milk-based drinks – as an example 90% espresso. If you tend to change your beans often, then a machine with a PID temperature controller is important. Also, if you are the only person in your household that makes espresso, a single boiler can work fine.