I actually went onto the Nintendo website and they said to do this if everything else is 'ok' -- Just pushing the buttons once instead of holding them on.
"Inside each of these compartments is a small red SYNC button – push and release this button on the Wii Balance Board once and also push the button on the Wii console once. You’ll see the light on the Power Button of the Wii Balance Board flash. Once the light has finished flashing and remains lit the synchronisation is complete and you’re ready to go."