Do note that if you choose this method for the LG G3 that runs on a stock recovery you will also end up in hard resetting your device – therefore before doing anything else backup your personal data, info and accounts along with anything else you might need afterwards.
1. Turn off your phone – you can press power button once for selecting “power off” or you can press and hold the power key for about 5 or 6 seconds.
2. Now, press and hold Power and Volume down buttons at the same time.
3. When the LG logo appears, release the keys.
4. Immediately press Power and Volume Down buttons again until the Hard Reset menu will be displayed.
5. Press Power button once and confirm the hard reset operation (this will not be necessarily if your LG G3 is running on a custom recovery image).
6. That’s it; now your LG G3 will boot into recovery mode.