IMG 2027

Here's a close up of the labeled 24 VAC relays which are controlled by nest thermostats in each of the zones and which control the TACO panel.  These relays are powered by a separate 24 VAC transformer seen on the right bottom side of the enclosure. This transformer provides power to the relay coils, switched by the zone thermostats.  The Taco zone panel, when it was originally connected directly to the Nest thermostats caused significant valve chattering probably due to its power-stealing strategy.  The Taco panel zone relays are powered by a separate (third) on board transformer and their coils are switched on and off by the zone panel relays, isolating the Taco panel entirely from the Nest thermostats.