Ignore the key, this is a chart of group surface temperature (degrees celsius) over time (minutes), commencing at the same moment that the LONDINIUM I is switched on
This is a morning start, the machine having been left off overnight, so the initial group surface temperature of approximately 24C is a good indicator of the ambient temperature
The method is to wait for the boiler to fully pressurise and the element to switch off
Then open the steam wand for 5 seconds to ensure no false pressure is in the system
Wait for the element to return the boiler pressure to 1.2bar and the element to switch off
Then pull hot water through the group until the solenoid opens to refill the boiler (indicated by the green light coming on) and promptly raise the lever to stop the flush
Wait for the boiler to fill (green light switches off) and the element to reheat the boiler and switch off again
Then repeat the process above for a second and third flush
All up to temp in less than 9 minutes
In the above chart I then left the machine until almost the 21st minute before pulling the first shot to show how far the group temp drops from its peak of around 86C as the heat from the 3rd flush distributes itself throughout the group. Ideally a short fourth flush could have been pulled, but the above chart serves to illustrate the point
So the first shot was pulled with a group surface temperature of around 81C, which is cooler than ideal, but still produces an espresso that is fit to drink – remember that the peak inlet temperature of the water will be much greater than 81C
Finally, you can see the effect of pulling a 60mL flush during the 23rd minute