Four-Zone Switching Relay with Priority, 120 VAC

Taco SR504 Four-Zone Switching Relay – 120V Control Panel for Hydronic Circulator Management

The Taco SR504 is a four-zone switching relay panel designed for use in hydronic heating systems that require independent control of multiple circulators. It accepts signals from up to four thermostats and activates the corresponding 120V circulator relay outputs while simultaneously managing boiler control via an isolated end switch.

This unit is ideal for zoning with circulator pumps and is compatible with both conventional and programmable 24V thermostats. LED indicators provide real-time status of calls for heat, circulator activity, and priority zone function. The SR504 simplifies wiring, reduces field errors, and supports integration with Taco’s full line of circulators.

Product Features

• Four Zone Capability: Independently controls up to four circulator pumps
• Isolated End Switch: Provides boiler or system signal when any zone is active
• Switchable DHW Priority: One zone can be assigned domestic hot water priority with timed override
• LED Diagnostics: Front-mounted indicator lights show zone call, end switch, and priority status
• Snap-In Relays: Enclosed plug-in relays allow for quick field replacement
• Contractor-Friendly Board Layout: Simplifies thermostat and circulator wiring
• Factory Tested: 100% tested for reliability and correct operation
• UL Listed: Complies with safety and electrical standards for field installations

Technical Specifications

• Model: SR504-4
• Input Voltage: 120 VAC
• Thermostat Input: 24 VAC
• Circulator Outputs: Four independent 120V outputs
• End Switch Output: 24 VAC dry contacts
• Mounting: Wall-mounted steel enclosure with knockout entries

Installation Notes

The SR504 is engineered for simplified installation in multi-zone hydronic heating systems. All terminals are clearly labeled to facilitate correct wiring of thermostats, circulators, and boiler controls. Installation should be completed by a licensed HVAC or plumbing technician to ensure compliance with local codes and correct system operation.

Application Scope

Commonly used in residential and light commercial hydronic systems where each zone is served by a dedicated circulator. The SR504 supports direct integration with boilers, indirect water heaters, and a variety of thermostat types for flexible zone control in baseboard, radiant, or panel heating systems.