Taco 3-Zone Switching Relay with Priority, SR503-4

Taco 3-Zone Switching Relay with Priority, SR503-4

The SR503-4 from Taco is a 3-Zone Switching Relay with Priority. It combines clearly labeled PC board layout with advanced features that allow for total system customization. External indicator lights provide instant diagnostic feedback, making a snap of service calls or new installation start-ups. Taco SR503 switching relays are UL and CSA listed, use standard “ice cube” replaceable relays and are compatible with conventional and programmable thermostats.


  • External Indicator Lights;
  • Switchable Priority;
  • Simplified Wiring;
  • Fully Enclosed Snap-Out Relays;
  • Compact Design;
  • Fuse Protected;
  • 100% Factory Tested;
  • Isolated End Switch;
  • Contractor Friendly PC Board Layout;
  • Universal Thermostat Compatibility;
  • UL and CSA Approved;
  • 24 Volt Power Input or Output Terminal;
  • Made in the USA;

Technical Specifications:

  • Zones: 3;
  • Power: 120VAC;
  • Max combined load: 15.0 AMPs;
  • Dimensions: 10.25" wide x 6.75" high x 2.75" deep.


  • Extended 3 Year Warranty; 
Product Specs
Application Zoning
Depth (Inches): 2-3/4"
Height (Inches): 6.75
Power Method: 120 VAC Input
Type1 Switching Relay
Voltage 120 VAC
Zones 3

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  • Taco 3-Zone Switching Relay with Priority, SR503-4 QR Code
  • Model: SR503-4
  • MPN: SR503-4
  • Availability: 74
  • $ 0.00


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Tags: Switching Relays, Heating Accesories, Hydronic Heating, Heating Supplies, Radiant Heating System, Heating and Cooling