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SR504-EXP-4 has been discontinued
Discontinued August 7, 2025
This product was discontinued by the manufacturer.
This item replaces: SR504-EXP-1
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Product Highlights
–
120 VAC Input
4
10-1/4" Width
6.75" Height
2-3/4" Depth
20 Amps
Description
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Taco Switching Relays combine clearly labeled PC board layouts with advanced features that allow
for total system customization. Whether using basic priority switching or the advanced features
of the -EXP controls, the job is made easy. External indicator lights provide instant diagnostic
feedback, making a snap of service calls or new installation start-ups. All switching relays are UL
and CSA listed, use standard "ice cube" replaceable relays and are compatible with conventional
and programmable thermostats.
Whether you want to expand up to 20 zones or utilize the advanced features of the PowerPort Cards and Add-on Power Controls, Taco -EXP controls allow for simple integration of advanced features. Plug in any combination of cards and controls to optimize the operation of any system.
Features include:
Additional -EXP Features
Whether you want to expand up to 20 zones or utilize the advanced features of the PowerPort Cards and Add-on Power Controls, Taco -EXP controls allow for simple integration of advanced features. Plug in any combination of cards and controls to optimize the operation of any system.
Features include:
- 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
- Extended 3 Year Warranty
- Made in the USA
Additional -EXP Features
- Plug-in PowerPort Card Slots
- Add-on Power Control Plug
- Expandable to 20 Zones
- Interface with -EXP Zone Valve Controls
Specs
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| Application: | Zoning |
|---|---|
| Number of Zones: | 4 |
| Width (Inches): | 10-1/4" |
| Height (Inches): | 6.75" |
| Depth (Inches): | 2-3/4" |
| Amperage: | 20 |
| Power Control Plugs: | 1 |
| 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
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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
TacoNeed help finding a replacement part?
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Product Reviews
4.85 out of 41 reviews
97% would recommend this product
5 star
90%
4 star
7%
3 star
0%
2 star
2%
1 star
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Customer Images
Most Liked Positive Review
Taco 503exp-4
this product looks better quality made than the 503 exp. version we had that came with our boiler when we purchased it , just hope it lasts longer and is more reliable that the old one , the pc board burned up in the old one causing the furnace to run and stop every 5 minutes. Just was a little confusing on wiring it up , so had my furnace man come and make sure it was wired up ok before firing it back up.
VS
Most Liked Negative Review
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Old Product
I was sent a taco relay that was from 2013
Showing 1-10 of 41 reviews
Old Product
I was sent a taco relay that was from 2013
Kev
Massachusetts
2 years ago
Verified Buyer
Was this review helpful to you?
yes I will
I do a lot of boiler work and this product is so easy to use for pump zoning.and Ihave orderd other products with fast shipping.
Jerry
ohio.
3 years ago
Verified Buyer
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Definitely recommend
Fast shipping, easy search and checkout process!
Jr
New England
3 years ago
Verified Buyer
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Solid product
Great way to incorporate all switching components and clean up the control panel.
Boiler Paul
Chicago
3 years ago
Verified Buyer
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good control
came with internal board pegs broken had spares
Captin Karl
Kingston NY
4 years ago
Verified Buyer
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Good services and product
Good services and product
Geno
MA
4 years ago
Verified Buyer
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terrific
works as expected
Dan
Severna Park MD
4 years ago
Verified Buyer
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These Taco Exp controls are night and day improved!
No more problems with boards burning up. Has a place for therm c-wire hook up. Fuses on every zone and all solid state. Post purge now built in. Circ exercising built in. Close to perfect.
Scott Thomas
Orono,Maine
4 years ago
Verified Buyer
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Perfect for my needs
Works perfectly. Built a combo domestic hot water system with radiant heating loop with primary pump and (3) secondary zone pumps. Utilized the 4th zone to input my domestic water switch to activate the primary pump. Works flawlessly.
Dustin
Kansas City
5 years ago
Verified Buyer
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I will continue to buy this product. Great company.
I have installed many radiant systems for myself and friends. I have never had one fail, and when I accidentally order the wrong one, Supply House gives me the best service ever !
Jeff W.
Caledonia Mi
6 years ago
Verified Buyer
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Product Q&A
15 Questions15 Questions
Q: i want to run the thermostats and circ. pumps independant of the boiler, the biomass boiler is completly controlled by the internal water temp will the unit handel this application
Asked by ian 16 years ago
Add your answer
Verified Reply- PexSupply StaffYes, you will not hook the switching relay's end switch to anything.
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Q: I currently have a SR503 switching relay and am adding 4 more zones. I would like to buy a SR504-EXP so I can add a reset controller later on but am woundering if I can use the expandable as my master and use the current sr503 as the slave but am not sure how to wire it or if its possible?
Asked by Chad 16 years ago
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Verified Reply- PexSupply StaffYou cannot do what you are describing, as you can only connect EXP's to EXP's.
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Q: i want to install an SR503 switching relay to our heating system, does it get mounted directly to the exterior of the boiler or on the nearest wall? Also, do I need zone valves when i have individual pumps for each zone?
Asked by 16 years ago
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Verified Reply- PexSupply StaffThe control can be mounted where ever you like. In regards to your second question, you do not need zone valves when zoning by circulators.
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Q: I purchased this item from Pexsupply recently. Two ? 1)what is ment by 24v input or output, how can it be both? 2)when heat is called for a circulator will be turned on, but I also want the heat exchanger circulator to turn on, where do i attach the exchanger circulator? Thanks
Asked by DJ 16 years ago
Add your answer
Verified Reply- PexSupply StaffThere is transformer on this relay that allows the 24 Volt Power Input or Output Terminal. Please take a look at the instruction sheet: http://s3.pexsupply.com/manuals/1286551201705/40322_PROD_FILE.pdf As for the heat exchanger, the location depends on your piping system. Please contact your installer for suggestion on the location of your heat exchanger.
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Q: what is the tt on my boiler i believe it is the thermastat but i must be sure
Asked by jj 16 years ago
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Verified Reply- PexSupply StaffTT stands for Thermostat.
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