Taco®, SR503, Switching Relay, 120 VAC, 15 A, DPDT

Taco SR503 Three-Zone Switching Relay – 120V Input, 3 Circulator Control

The Taco SR503 is a 3-zone switching relay designed to manage up to three separate circulator pumps in hydronic heating systems. Engineered for use with 24V thermostats, this control panel simplifies zone-based installations and ensures reliable coordination between zone calls and pump operation.

This relay is commonly used in multi-zone hot water heating systems and supports integration with Taco 00 series circulators. The SR503 provides installer-friendly wiring terminals, diagnostic LEDs for troubleshooting, and an isolated end switch for boiler or system control.

Product Features

• Zones: Controls up to 3 circulator pumps independently
• Power Input: 120 VAC
• Thermostat Control: Compatible with standard 24 VAC thermostats
• End Switch: Isolated end switch for external boiler or primary pump control
• LED Indicators: Visual diagnostics for each zone and power status
• Priority Zone Setting: Optional DHW priority zone function (Zone 1)
• Relays: Enclosed, snap-out design for easy replacement and protection
• Factory Tested: 100% factory tested for function and reliability

Technical Specifications

• Model: SR503
• Zones: 3 circulator outputs
• Voltage Input: 120 VAC, 60 Hz
• Thermostat Inputs: 3 x 24 VAC
• Pump Output: 3 x 120 VAC circulator circuits
• Priority Function: Selectable for Zone 1
• Dimensions: 11-1/4" W x 7" H x 3-3/4" D (approx.)

Installation Overview

The Taco SR503 is designed for fast installation and system expansion. Wiring terminals are clearly labeled, and the compact enclosure allows for wall or panel mounting. The unit is best installed by licensed contractors familiar with low-voltage thermostat controls and line-voltage pump wiring. All connections should comply with local electrical codes.

Professional Use

The SR503 is widely used in residential and light commercial hydronic systems, offering streamlined zone pump management with built-in diagnostics and compatibility across a range of control scenarios. Ideal for systems requiring dedicated circulator operation per heating zone.