Yes, the relay controls have the ability to prioritize DHW demand and they also have the ability to operate a specific pump for DHW demand. This can be done with the Caleffi ZSR Z-one switching relay or the ZVR Z-one valve relay.
"Priority" logic is DIP switch configurable on the board. During "priority", when the DHW aquastat energizes to call for heat, the relay control disables the space heating outputs and all the boiler energy is used to heat the DHW tank. When the DHW tank is satisfied, the space heating is re-enabled.
The Caleffi Z-one Wiring Guide shows wiring schematics and piping schemes for many common applications, including priority control. And, our archived Zone Relay Controls for Hydronic Heating Coffee with Caleffi webinar from February 2016 covers all the features and functionality of the relays, including the new 2016 enhancements. Take a look at these great resources, at your convenience.
Contact your local Caleffi supplier if you have any questions about applying the Z-one Relays; we appreciate your business!