Two-Zone Switching Relay with Priority, 120 VAC

Taco SR502-4 Two-Zone Switching Relay – Dual-Circulator Control for Hydronic Heating Systems

The Taco SR502-4 is a two-zone switching relay panel designed to provide independent 120V control of two circulators in hydronic heating applications. Compatible with standard 24V thermostats, it integrates directly with boiler and zone systems, streamlining multi-zone configuration and operation.

This relay features an isolated end switch for boiler activation, front-facing diagnostic LEDs for real-time system monitoring, and a contractor-friendly layout to reduce wiring complexity. It includes a built-in priority function for domestic hot water systems or other designated zones and supports field replacement of relays and transformers for long-term maintainability.

Key Features

• Independent Two-Zone Control: Supports two circulators with individual thermostat inputs
• Isolated End Switch: Activates boiler upon demand from any active zone
• Switchable Priority Zone: Enables priority function for DHW or critical zone with timeout option
• LED Indicators: Display call status, power, and relay activity for simplified diagnostics
• Contractor-Friendly Terminal Layout: Clearly labeled connections reduce field wiring errors
• Factory-Wired and Tested: 100% tested prior to shipment for performance and safety
• Snap-In Relay Modules: Enclosed relays can be easily replaced in the field
• UL Listed: Meets safety standards for HVAC applications

Technical Specifications

• Model: SR502-4
• Zones: 2
• Input Voltage: 120 VAC
• Thermostat Input: 24 VAC
• Circulator Outputs: Two 120V circulator outputs
• End Switch Output: 24V dry contacts
• Protection: Fuse protected with field-replaceable transformer

Installation Considerations

The SR502-4 is intended for wall-mounted installation in residential or light commercial hydronic systems. Designed to reduce setup time, it features labeled terminals, LED indicators, and compact construction. Installation should be completed by qualified professionals familiar with line-voltage HVAC wiring and system zoning requirements to ensure code compliance and safe operation.

Typical Applications

Ideal for use in two-zone baseboard heating systems, radiant heating circuits, or combination boiler/DHW configurations. Commonly deployed in systems where precise control of multiple circulators is needed to improve thermal distribution and zoning efficiency.