Taco Zone Valve Controls work with two-, three-, or four-wire zone valves. All are fuse protected; it also includes two isolated end switches and a built-in priority switch. The contractor friendly PC board layout eliminates incorrect wiring and the "unfinished" look of conventional zone valve installations. The sturdy screw connections add even more reliability, while the external indicator lights provide instant diagnostic feedback to reduce installation time and troubleshooting. The Taco Priority Zoning Circulator can be used in conjunction with other circulators or zone valves, and is ideal for indirect hot water heaters, adding another zone, zoning with circulators, and for prioritizing under-sized zones. They are available in a full range of sizes from 003-0014 to match your specific system requirements. Expandable Zone Control Valve Features: Expandable to 120 Zones (20 Zone Panels); Includes the Priority Zoning Circulator, Configurable Dipswitches, Compatible with Conventional and Programmable Thermostats, UL Listed, Switch to Override Power Controls, Microprocessor Controlled, Field Replaceable Transformer, Fuse Protected, 2 Boiler Enabled End Switches Space Heating and DHW, Contractor Friendly PC Board Layout and Premium Sealed Relays.