Charge 2 won't sync after upgrading iPhones

[Blossom62]

Updated my iPhone today and although my personal details have transferred, my fitbit Charge 2 won't sync. Have deleted and reinstalled app, as well as turning phone off and back on to no avail. Help!

Moderator edit: updated subject for clarity

[MarreFitbit · Accepted solution]

Hey there @Blossom62, it's nice to see you here! Thanks for already troubleshooting this syncing issue between your Charge 2 and your new iPhone S6, nice way to go!  

Syncing difficulty is usually caused by a missing requirement. Verify each requirement before moving on to the troubleshooting steps.

• The latest version of the Fitbit app is installed on your phone.
• The software on your iPhone is up to date. To check, tap Settings > General > Software Update.
• The Bluetooth setting on your iPhone is on. To check, tap Settings > Bluetooth.
• Your iPhone isn't managing other Bluetooth connections. For more information, see Is the Fitbit app for iOS interfering with other Bluetooth devices?
• If you use more than one device to sync, make sure the other device isn't nearby or that the old iPhone isn't nearby. If the device is nearby, turn off Bluetooth on it. For more information, see Why won't my Fitbit device sync to another phone or computer?​
• Your Fitbit device's battery isn't critically low.

If your device still won't sync, try these steps:

1. Force quit the Fitbit app. 
2. Go to Settings > Bluetooth and turn Bluetooth off and back on.
3. Open the Fitbit app.
4. If your Fitbit device didn't sync, restart your iPhone. 
5. Open the Fitbit app.
6. Restart your Fitbit.
7. If your Fitbit device won't sync after the restart, log in to your Fitbit account on a different phone, tablet, or computer and try to sync.
8. If your Fitbit device still doesn’t sync, remove all other Fitbit devices from your account and from the list of connected Bluetooth devices on your iPhone and try to sync.

Give this a shot and let me know the outcome! 

[useless-device]

I followed all these instructions, and my iphone will not find my fully charged Charge2

[anotherjosh]

I had the same problem.  I ended up discovering that my watch was still pairing with my old phone.  I turned off Bluetooth on my old phone and then paired my Charge3 with my new phone.