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SR503-4 has been discontinued
Discontinued May 12, 2026
This product was discontinued by the manufacturer.
MANUALS (3)
This item replaces: SR503-5, SR503-2, SR503
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Direct Replacement:
3 Zone Next Generation Switching Relay w/ Priority, Expandable
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Product Highlights
–
120 VAC Input
3
10-1/4" Width
6.75" Height
2-3/4" Depth
120v
Description
–
The Taco SR503-4 Switching Relay is the best choice for all your zoning needs, with advanced PowerPort Cards, external diagnostic lights, switchable priority and contractor friendly PC board layouts. Combined with the time proven reliability of the 00 family of circulators and thermostats, total system integrating is achieved. External indicator lights provide instant diagnostic feedback, making a snap of service calls or new installation start-ups.
- 24-Volt power input or output terminal
- Fuse protected
- Simplified wiring
- Compact design
Specs
–
| Application: | Zoning |
|---|---|
| Number of Zones: | 3 |
| Width (Inches): | 10-1/4" |
| Height (Inches): | 6.75" |
| Depth (Inches): | 2-3/4" |
| Power Method: | 120 VAC Input |
| Voltage: | 120v |
Questions?
Speak with a real person who will go out of the way to help!
Call or text 888-757-4774
Monday – Thursday
8am–7:45pm
Friday
9am–7:45pm
Saturday – Sunday
9am–5:45pm
Compare Similar Products
Brand
Number of Zones
You May Also Need
3 Replacement Parts
Replacement Fuse - 5 Amp (10 Pack)
SKU: SR5A-005RP
TacoReplacement Fuse - 1 Amp (10 Pack)
SKU: SR1A-001RP
TacoReplacement Fuse - 6 Amp (10 Pack)
SKU: SR6A-001RP
Taco
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Product Reviews
4.86 out of 50 reviews
98% would recommend this product
5 star
90%
4 star
8%
3 star
0%
2 star
2%
1 star
0%
Customer Images
Most Liked Positive Review
Great product /shopping experience
Ordered on Friday, it arrived on Monday. Very easy to set up. Rather self explanatory. Thanks to the Supply House staff for walking me through the order to make sure I picked the correct unit.
VS
Most Liked Negative Review
ZC-ZR relay cannot be controlled by external input.
Electronic boiler controllers hace a circulator holdoff function that prevents the circulators from running until the boiler reaches a minimum operating temperature. This can be accomplised by activating the ZC/ZR relay in the 3-zone switching relay by a 120 VAC signal from the boiler control. If this feature were provided on the Taco switching relay, then the circulator enable signal on the boiler control would not have to carry the load current of multiple circulators. Also, the circulator relays on the Taco unit look a little light to handle the inrush current of a B & G series 100 pump.
Showing 1-10 of 50 reviews
Exactly What I Needed. Shipped Quick
Needed a replacement and this was exactly what I needed. Best price for the quick shipping needed. Would use Supply House again
George
Ridgefield, CT
2 years ago
Verified Buyer
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I would order from hear again.
Fast delivery and reasonable pricing. Only issue is that I got 1/2 inch copper 90s. I ordered and was billed for 3/4 inch copper 90s.
Jason
Ebensburg, Pa
2 years ago
Verified Buyer
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First class business
Great customer service and fast shipping. I love their service.
Pineapple
Acme, PA
3 years ago
Verified Buyer
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Yes
Great product
Best price online
Walter
NJ
4 years ago
Verified Buyer
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works great for application
run heat pumps for hydronic system
Abner
NE Iowa
4 years ago
Verified Buyer
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I'll buy it again
Professional use
Plumber
Vermont
4 years ago
Verified Buyer
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Yes
Loved it
West
Bayshore Long Island
4 years ago
Verified Buyer
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I would buy again
Works great
Cps
Salisbury Maryland
4 years ago
Verified Buyer
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Great company
Easy ordering online. Fast delivery. Item was as described and worked perfectly.
Linda
Babylon, NY
5 years ago
Verified Buyer
Was this review helpful to you?
ZC-ZR relay cannot be controlled by external input.
Electronic boiler controllers hace a circulator holdoff function that prevents the circulators from running until the boiler reaches a minimum operating temperature. This can be accomplised by activating the ZC/ZR relay in the 3-zone switching relay by a 120 VAC signal from the boiler control. If this feature were provided on the Taco switching relay, then the circulator enable signal on the boiler control would not have to carry the load current of multiple circulators. Also, the circulator relays on the Taco unit look a little light to handle the inrush current of a B & G series 100 pump.
Jack
Hartland, CT
5 years ago
Verified Buyer
Was this review helpful to you?
Product Q&A
5 Questions5 Questions
Q: Is this product compatible with Nest Thermostats. Having trouble setting up
Asked by Jean 8 years ago
Add your answer
Verified Reply- SupplyHouse StaffYes, it is
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Q: Does this relay need a transform or is it incorperated in the relay, to read the thermostat and start circulating pumps?
Asked by RP 9 years ago
Add your answer
Verified Reply- SupplyHouse StaffTaco switching relays have a transformer built in to power the thermostats.
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Q: Will this relay control a loop circulating pump that goes on when a zone pump is called to go on?
Asked by Russ 10 years ago
Add your answer
Verified Reply- Supplyhouse StaffYes it will, see the manual linked below: http://s3.supplyhouse.com/manuals/1351150925280/85270_PROD_FILE.pdf
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Q: I need a 3 zone switching relay that has 120VAC output for circulators not 24VDC. Is this a correct model?
Asked by Shane 10 years ago
Add your answer
Verified Reply- Supplyhouse StaffYes that is for controlling 120VAC pumps
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Q: I need a zone relay panel to control three circulator pumps in my home heating system. Is this the correct product?
Asked by Bob 11 years ago
Add your answer
Verified Reply- Supplyhouse StaffYes, that will work with 3 separate, circulator pumps.
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