Taco Switching Relays combine clearly labeled PC board layouts with advanced features that allow for total system customization. Whether using basic priority switching or the advanced features of the -EXP controls, the job is made easy. External indicator lights provide instant diagnostic feedback, making a snap of service calls or new installation start-ups. All switching relays are UL and CSA listed, use standard ice cube replaceable relays and are compatible with conventional and programmable thermostats. For larger jobs, switching relays can be expanded up to 20 zones with priority. With the exclusive Taco PowerPort Plug-In Cards, you can easily add such features as post purge, priority protection and pump exercise. Any expandable switching relay can also interface with the Boiler Reset Control and Injection Mixing Add-On Power Controls.