Nest - Solenoid on bypass humidifier not engaging - 16v output on *

Hi all, hoping someone can help. I cannot get NEST to activate the solenoid. Heat, Cool, Fan all work fine. I decided to measure the voltage for '*' from nest to 'C' on furnace terminal and get 16V. What do I need to do? Shouldn't nest be putting out 24V from '*"? --- 1. * (star) is connected to one end of the solenoid 2. Other end of the solenoid is connected to 'C' terminal at furnace. 3. 'C' is also run from the furnace to 'C' on nest.