This short video goes over how to back flush an espresso machine. The machine used is a Rocket Giotto but the same steps apply to any machine with a three way solenoid valve.
This demonstrates how to flush a “Mixer” type heat exchanger espresso machine for proper brew temperature. For more details, go to http://www.home-barista.com.
Chris from Smokey Barn Coffee Roasters explains this essential cleaning routine for espresso machines. http://smokeybarn.co.uk.