Originally Posted by E90Company
What he said, but make sure your air's heat is on full blast.
I'm fairly certain you need to have the heat temperature setting at it's highest (80 degrees) while the fan speed is set to it's lowest (1 bar) setting.
Turn off anything else in the car that is a drain on the battery. After your 10-15 second initiation period you should be able to hear clicking and bubbling from your coolant reservoir area.
The coolant flush takes about 13 min iirc, and it will cycle through several periods of pushing liquid and resting. If you start the car before then you won't hurt anything, you just won't get a full flush.
Also, I'd advise doing this on a cold engine, BEFORE the coolant system has built up pressure.