If your iron is left unused horizontally for more than 2 minutes, or vertically (on the heel rest) for more than 8 minutes, it switches off automatically for safety reasons.
When this happens, the red or blue automatic shut-off light flashes.
Pressing any button will turn the iron on and it will start heating up again.
After approx. 2 min. it will be ready for ironing.
If your iron is a pressurised steam generator (GC90xx): once you hear 2 beeps and the light on the active steam selection button stops flashing and stays on, you can start steam ironing by pressing the steam trigger (see chapter 'Using the iron' in the user manual).