Programmable Thermostat

The Taco SR503-4 is a professional-grade 3-zone enhanced switching relay designed for hydronic heating and cooling systems requiring multi-zone temperature control with priority operation. This circulator pump replacement component operates at 120 VAC, 60 Hz and delivers reliable performance in commercial and residential HVAC applications where zone management and system prioritization are essential. Built to handle demanding hydronic zoning requirements, the SR503-4 features a maximum amperage rating of 15 A with 1/3 HP capacity and DPDT (Double Pole, Double Throw) switching capability. The unit is housed in a NEMA 1 enclosure, providing protection suitable for indoor installation in control rooms, mechanical spaces, and equipment closets. With three independently controlled zones and priority switching functionality, this relay allows system operators to manage heating distribution efficiently while ensuring critical zones receive priority flow when demand exceeds system capacity. The SR503-4 is ideal for retrofitting existing hydronic systems or upgrading controls in multi-zone residential and light commercial applications. Its compact design facilitates easy installation in tight spaces, and the straightforward electrical connections integrate seamlessly with standard thermostat and pump control wiring. This replacement component helps restore system functionality and maintains precise temperature control across multiple building zones. Professional installers and building maintenance teams rely on Taco Comfort Solutions components for their durability, consistent performance, and compatibility with established hydronic system architectures. This SR503-4 relay represents a cost-effective solution for restoring zone control capability in systems requiring dependable multi-zone switching and priority operation.