There's an initialization sequence in the manual for resetting it.
But, here is the snippet of it.
To do a system reset:
Make sure the CCC 2 thermostat is in the OFF mode.
Simultaneously press the MODE and ZONE buttons. The LCD will display IniT and all available zones.
Release the MODE and ZONE buttons.
Press the ON/OFF button to exit system set up.
Make sure the unit displays both zones when it's initializing. If it doesn't, there's a communication problem with the zone that's not displayed.