Diagnosis
Bluetooth pairing has failed or the handle's Bluetooth module is stuck. This is a frequent glitch after app updates or phone OS changes.
How to Fix It
Delete the toothbrush from your phone's Bluetooth settings list. Then, in the Oral-B app, delete the brush from 'My Devices'. Perform a hard reset on the brush: hold the power button for 15 seconds until it vibrates and all lights flash. Start the pairing process fresh from the app.
If That Didn't Work
Ensure your phone's Bluetooth is toggled off, then on. Restart your phone. Attempt pairing with a different smartphone if possible to isolate the problem to your phone or the brush.
Heads Up
The brush only enters pairing mode for 2 minutes after being turned on from a full off state. If you miss that window, turn it off and on again to restart the pairing timer.