Taco - 3, 4, 6 Zone Expandable Switching Relay with Priority

The Taco SR-EXP Expandable Switching Relay is a multi-zone hydronic control panel designed to operate individual 120V circulator pumps from low-voltage thermostats. Available in 3-, 4-, and 6-zone configurations, each control includes switchable priority, built-in priority protection, boiler end switches, primary circulator control, post-purge, pump exercise, and external LED diagnostics. The expandable design allows up to 20 compatible zoning panels to be interconnected for systems containing as many as 120 zones. Compatible with conventional and programmable thermostats, Taco SR-EXP controls simplify wiring, troubleshooting, and boiler integration in residential and light commercial hydronic heating systems.

Taco — SR503-EXP-4: Three-zone expandable switching relay with priority

Taco — SR504-EXP-4: Four-zone expandable switching relay with priority

Taco — SR506-EXP-4: Six-zone expandable switching relay with priority

Usage

The Taco SR-EXP control is installed near the boiler as the central control panel for a hydronic system using one circulator pump per heating zone. Each thermostat connects to its corresponding low-voltage input. When a thermostat calls for heat, the control energizes that zone’s 120V circulator and closes the boiler end switch. The highest-numbered zone can be configured as a priority zone for an indirect domestic water heater. Multiple EXP controls can be linked as master and slave panels, while the primary-pump, post-purge, priority-protection, and pump-exercise functions are selected using the internal switches.