🛁 Grundfos 43 Series Spa Circulation Pump – 115V Single Speed 1″ Barb

Whisper-quiet, energy-efficient circulation for 24-hour spa filtration

📋 Product Overview

The Grundfos 43 Series (Model 31842) is a compact, energy-efficient spa circulation pump designed for 24-hour continuous filtration in portable hot tubs. Manufactured by Grundfos — one of the world’s most recognized names in pump technology — this single-speed circulator delivers 12 to 18 GPM through 1″ barb connections while drawing just 0.71 amps, costing only pennies per day to operate.

The 43 Series features Grundfos’ redesigned rotating volute that allows installation in virtually any plumbing configuration, making it one of the most versatile spa circulation pumps available. It runs on 115V/60Hz and operates at near-silent levels, ensuring a relaxing spa experience without disruptive pump noise. This pump is a direct replacement for the earlier Grundfos UP15-38SPA and also serves as a popular replacement for Laing E10 and Waterway Tiny Might circulation pumps using 1″ barb plumbing.

✨ Key Features

• ✅ Grundfos 43 Series Circulator – Built to Grundfos’ world-renowned standards for reliability and efficiency in spa circulation applications
• ✅ 12 to 18 GPM Flow Rate – Consistent water movement for effective 24-hour filtration and heat distribution
• ✅ Ultra-Low Energy Consumption – Just 0.71 amps / 82 watts — costs only pennies per day to operate continuously
• ✅ Whisper-Quiet Operation – Near-silent performance ensures no disruption to spa enjoyment
• ✅ Rotating Adjustable Volute – Redesigned wet end rotates to accommodate virtually any plumbing configuration
• ✅ 1″ Barb Connections – Standard 1″ barbed intake and discharge for secure connection to vinyl tubing
• ✅ Side Discharge Design – Discharge exits from the side of the pump body
• ✅ Compact and Lightweight – Space-saving footprint fits tight equipment compartments
• ✅ Includes Mounting Bracket – Grundfos mounting bracket allows flexible pump positioning
• ✅ Continuous Duty Rated – Designed specifically for 24/7 spa circulation operation
• ✅ Replaces Multiple Brands – Drop-in replacement for Laing, Waterway, and other circ pump brands with 1″ barb connections
• ✅ 36-Month Manufacturer Warranty – Grundfos factory warranty from date of manufacture

⚙️ Technical Specifications

Specification	Value
Model Number	31842
Manufacturer	Grundfos
Series	43 Series
Pump Type	Circulation
Grundfos Type	UP15-43SPA (replaces UP15-38SPA)
Grundfos Product Code	PUGR1543115S
Speed Settings	Single Speed
Voltage	115V
Frequency	60 Hz
Amperage	0.71A
Wattage	82W
Flow Rate	12–18 GPM
Suction Port	1″ Barb
Discharge Port	1″ Barb
Discharge Position	Side
Barb OD	Approx. 1.10″
Port Inside Diameter	Approx. 3/4″
Volute	Rotating/Adjustable
Cord	Not Included (Hardwire or AMP cord sold separately)
Mounting	Includes Grundfos mounting bracket
Drain Plug	Included (must be hand-tightened before installation)
Warranty	36 months from date of manufacture

🔌 Electrical Requirements

Electrical Spec	Requirement
Supply Voltage	115V
Frequency	60 Hz
Phase	Single Phase
Full Load Amps	0.71A
Wattage	82W
Connection	Hardwire or AMP plug cord (sold separately)

⚠️ IMPORTANT ELECTRICAL SAFETY INFORMATION:

• All electrical work must be performed by a licensed electrician in accordance with the National Electrical Code (NEC) and local building codes.
• Hot tubs and spas require GFCI (Ground Fault Circuit Interrupter) protection as mandated by the NEC.
• A dedicated circuit is required — do not share the circuit with other appliances.
• This pump does not include a power cord. A 1-speed AMP plug cord can be purchased separately, or the pump can be hardwired to your spa control system by a licensed electrician.
• This is a 115V pump. If your spa requires 230V, you need the Grundfos 43 Series 230V model (59896292 / PUGR1543220S) instead. Connecting to incorrect voltage will damage the pump.

🔄 Compatibility Guide

Connection Configuration

Specification	This Pump
Suction	1″ Barb
Discharge	1″ Barb (Side)
Barb OD	Approx. 1.10″
Tubing Size	1″ inside diameter vinyl tubing
Volute	Rotating — adjustable for multiple plumbing configurations

Stepping Up From 3/4″ Plumbing

If your existing spa uses 3/4″ vinyl tubing, you can upgrade to this 1″ barb pump by using barb-to-barb adapter fittings (such as part number 1429-131) available from plumbing supply stores.

Direct Replacement For

This pump directly replaces the following Grundfos models:

• Grundfos UP15-38SPA (all versions)
• Grundfos UP15-43SPA (all versions)
• Grundfos 59896864
• Grundfos 59896132
• Grundfos 59896223
• Grundfos 59896336
• Grundfos 59896352

Cross-Compatible With

The Grundfos 43 Series is widely used as a replacement for other brand circulation pumps with 1″ barb connections:

• Laing E10 (74069 / 6050U0011) — with matching barb size
• Waterway Tiny Might — with matching barb size
• Other 1″ barb circulation pumps of similar flow and voltage

⚠️ Always verify your existing pump’s connection type (barb vs. union vs. threaded), connection size, and voltage before ordering a replacement.

Voltage Variants

Model	Voltage	Part Numbers
31842 / 59896291 (this pump)	115V / 60Hz	PUGR1543115S, 10-0134
59896292	230V / 60Hz	PUGR1543220S, 10-0135

Alternate Part Numbers

This pump may also be referenced under the following part numbers:

• UP15-38SPA
• UP15-43SPA
• PUGR1543115S
• 59896291
• 59896352
• 59896132
• 59896864
• 59896223
• 59896336
• 70813 (Watkins)
• PU602393 (Hurricane)
• 10-0134 (HydroQuip)
• 9333-01
• 1-00-0046
• 34-430-2050
• 1-00-0184
• GG92007
• 15-178-6291
• LB303611
• 1030005
• 0P21001-19 (Artesian Spas)

🔧 Installation Requirements

Mounting

Requirement	Specification
Mounting Position	Flexible — mounting bracket included
Base	Solid, level surface
Ventilation	Maintain adequate clearance around the pump body
Access	Allow clearance for plumbing connections and drain plug

Plumbing

Connection	Size
Suction	1″ Barb
Discharge	1″ Barb (Side)
Tubing	1″ ID vinyl tubing

Installation Notes

⚠️ DRAIN PLUG: Grundfos ships these pumps with the drain plug installed loosely. You must hand-tighten the drain plug before installing the pump. Do not over-tighten — hand-tight only.

⚠️ Do not run the pump dry. Always ensure the pump casing is filled with water before starting.

⚠️ The rotating volute allows the discharge to be oriented in multiple directions for flexible plumbing configurations. Rotate the volute to align with your existing plumbing before securing.

⚠️ GFCI protection is required by the National Electrical Code (NEC) for all hot tub and spa installations.

⚠️ This pump does not include a power cord. Purchase an AMP plug cord separately or hardwire to your spa control system.

⚠️ When replacing a 3/4″ barb pump, use barb-to-barb adapters (such as part 1429-131) to step up to the 1″ barb connections, along with appropriate 3/4″ ID tubing if needed.

⚙️ Maintenance Guide

Routine Maintenance

Task	Frequency	Notes
Check for leaks	Monthly	Inspect barb connections and drain plug
Inspect barb connections	Monthly	Ensure hose clamps are secure
Verify drain plug tightness	Quarterly	Hand-tight only
Check amperage draw	Annually	Should read approximately 0.71A
Inspect mounting bracket	Quarterly	Tighten if vibration has loosened bolts
Clean pump intake	As needed	Remove debris that may restrict flow

Warning Signs — Consider Pump Replacement If:

• Unusual noise (grinding, humming, or buzzing)
• Water leaking from the pump body or connections
• Motor trips breaker repeatedly
• Noticeably reduced water flow
• Motor running hot or failing to start
• Pump not maintaining circulation after priming

🎯 Ideal Applications

Application	Suitability	Notes
♨️ 24-Hour Spa Circulation	✅ Yes — Primary Use	Designed specifically for continuous spa filtration
♨️ Spa Heating Circulation	✅ Yes	Maintains consistent water flow through heating system
♨️ Chemical Distribution	✅ Yes	Continuous movement ensures even sanitizer distribution
♨️ Ozone System Circulation	⚠️ Caution	Do not introduce ozone directly to pump suction — air locking may occur
♨️ Replacement for Laing E10	✅ Yes	Popular upgrade/replacement with 1″ barb connections
♨️ Replacement for Waterway Tiny Might	✅ Yes	Compatible with 1″ barb plumbing systems
♨️ Hot Springs / Watkins Spas	✅ Yes	OEM part number 70813 for Watkins applications
♨️ Jet Pump Application	❌ No	This is a low-flow circulation pump — it does not power therapy jets
♨️ 1-1/2″ Union Plumbing	❌ No	Uses 1″ barb connections — not compatible with union-style plumbing without adapters

❓ Frequently Asked Questions

Q: What horsepower is this pump? A: The pump is listed at approximately 1/15 to 1/16 HP (0.06–0.0625 HP), drawing 0.71 amps and 82 watts. For replacement matching, use the amperage and wattage ratings rather than HP, as horsepower ratings can vary between sources.

Q: Will this fit my hot tub? A: This pump uses 1″ barbed connections for vinyl tubing. Check your existing circulation pump’s connection type and size. If your current pump uses 1″ barbs, this is a direct fit. If you have 3/4″ barb plumbing, you’ll need barb-to-barb adapter fittings.

Q: What voltage does this pump require? A: 115V / 60Hz. If your spa requires 230V, you need the Grundfos 230V version (59896292 / PUGR1543220S). Always verify voltage before ordering.

Q: Does this come with a power cord? A: No. The pump does not include a power cord. You can purchase a 1-speed AMP plug cord separately or have a licensed electrician hardwire the pump to your spa control system.

Q: What is the flow rate? A: 12 to 18 GPM, depending on system resistance (plumbing length, fittings, elevation changes).

Q: Can I use this as a replacement for a Laing E10? A: Yes. The Grundfos 43 Series is a popular and widely used replacement for Laing E10 circulation pumps with 1″ barb connections. Many spa technicians recommend it as a reliable, cost-effective alternative.

Q: Can I use this as a replacement for a Waterway Tiny Might? A: Yes, if your Tiny Might has 1″ barb connections and runs on 115V. Verify connection type and size match before ordering.

Q: What is the rotating volute feature? A: The redesigned volute can be rotated to position the discharge in multiple directions, allowing the pump to be installed in virtually any plumbing configuration without additional fittings or modifications.

Q: Do I need to tighten the drain plug? A: Yes. Grundfos ships the pump with the drain plug installed loosely. You must hand-tighten the drain plug before installing the pump in your spa.

Q: Can I use ozone with this pump? A: Do not introduce ozone directly to the pump suction, as air locking may occur. Route ozone injection downstream of the circulation pump.

Q: What warranty is included? A: Grundfos provides a 36-month warranty from date of manufacture. Contact Parts4Tubs for full warranty terms and conditions.

Q: Do I need a GFCI breaker? A: Yes. GFCI (Ground Fault Circuit Interrupter) protection is required by the National Electrical Code (NEC) for all hot tub and spa installations.

Q: Is this pump compatible with my Watkins/Hot Springs spa? A: Yes. This pump is referenced under Watkins part number 70813 and is used as OEM equipment in many Watkins/Hot Springs models.

🏆 Why Choose the Grundfos 43 Series

• ✅ Grundfos Quality — World-renowned pump manufacturer with decades of proven reliability
• ✅ Whisper-Quiet Operation — Near-silent performance for undisturbed spa enjoyment
• ✅ Ultra-Low Operating Cost — Just 82 watts / 0.71 amps — costs pennies per day to run continuously
• ✅ Rotating Volute Flexibility — Adjustable discharge direction fits virtually any plumbing layout
• ✅ Broad Cross-Compatibility — Replaces Grundfos, Laing, Waterway, and other 1″ barb circ pumps
• ✅ Compact and Lightweight — Fits tight equipment compartments with ease
• ✅ OEM Trusted — Factory-installed in spas from Watkins, Hot Springs, Hurricane, Artesian, and more
• ✅ 36-Month Factory Warranty — Grundfos-backed manufacturer warranty for peace of mind

🤝 Why Buy From Parts4Tubs

• ✅ US-based support for American customers
• ✅ Fast shipping across the United States
• ✅ Expert advice from spa and hot tub specialists
• ✅ Competitive pricing in USD
• ✅ Full warranty support
• ✅ Hassle-free returns
• ✅ Compatible AMP cords and adapter fittings available
• ✅ Dedicated customer service team

💧 Summary

The Grundfos 43 Series (Model 31842) is a whisper-quiet, ultra-efficient single-speed spa circulation pump running on 115V/60Hz at just 0.71 amps. Delivering 12–18 GPM through 1″ barb connections, it features Grundfos’ innovative rotating volute for flexible installation in any plumbing configuration. This pump directly replaces Grundfos UP15-38SPA models and cross-references to Laing, Waterway, Watkins, HydroQuip, and other OEM applications, backed by a 36-month Grundfos factory warranty. Order today from Parts4Tubs for fast US shipping and expert support.

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	Magic Plastics Union 0602-15 (1.5″ Pump Union) | 1-1/2″S x 1-1/2″FBT Union, Pump, Magic, 1-1/2"S x 1-1/2"FBT (Industry Standard) w/ O-Ring	$6.36 Max: 586 Min: 1 Step: 1 Add to cart
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Hot Tub Pump Collar & Union Size Chart

Imperial & Metric Specifications

Union Size	Collar Size	Thread OD	Union OD	O-Ring Size
1.5" Female Buttress Thread (FBT)	2.5" / 64mm (Tip to Tip) Measurement	2-1/2" 64mm	2-13/16" 71mm	2-5/16" OD 59mm
2" Female Buttress Thread (FBT)	3.1" / 78mm (Tip to Tip) Measurement	3-1/16" 78mm	3-3/8" 81mm	2-15/16" OD 75mm
2.5" Female Buttress Thread (FBT)	3.6" / 91mm (Tip to Tip) Measurement	3-5/8" 91mm	4-1/4" 108mm	3-7/16" OD 87mm

Important Notes

The union "size" (1.5", 2", 2.5") is nominal and doesn't correspond to any actual measurement.

Collar size is measured from thread tip to thread tip on the pump outlet.

Most hot tub pumps use Female Buttress Thread (FBT) - 98% of applications.

O-ring gaskets may vary between manufacturers - measure your existing gasket for accuracy.

How do I Replace a Hot Tub Pump?

Here's a general step-by-step guide on how to replace a hot tub pump. Keep in mind that the specific steps may vary depending on your hot tub's make and model, so it's essential to consult your hot tub's manual for model-specific instructions. If you're not comfortable with this procedure, it's a good idea to seek professional assistance.

Materials You'll Need:

• Replacement pump
• Pipe wrench
• Adjustable wrench
• Screwdriver
• Pipe sealant (thread tape or plumber's putty)
• PVC primer and cement (if you have PVC plumbing)
• Teflon tape (for threaded connections)

Procedure:

1. Turn Off the Power: Before you begin, ensure the hot tub's power supply is turned off at the circuit breaker or disconnect switch. Safety should always be a priority when working with electrical components.

2. Drain the Hot Tub: If your hot tub is not already empty, you'll need to drain it. Follow your hot tub's manual or manufacturer's instructions for proper draining. (You might not need to do this if you can lock the pump off with the gate valves)

3. Locate the Pump: Identify the location of the existing pump in your hot tub. It's usually located near the equipment area or in a designated pump compartment.

4. Disconnect the Electrical Wiring: Carefully disconnect the electrical wiring from the old pump. This typically involves removing the electrical conduit cover, unscrewing wire nuts, and disconnecting the wires from the terminals. Be sure to note the wire connections or take a picture for reference when connecting the new pump.

5. Disconnect the Plumbing: Depending on your hot tub's plumbing setup, you'll need to disconnect the plumbing connections to the pump. Use a pipe wrench or adjustable wrench to loosen and remove the fittings. Be prepared for some water spillage when disconnecting the plumbing.

6. Remove the Old Pump: Once the electrical and plumbing connections are detached, carefully remove the old pump from its mounting position. Some pumps may be secured with mounting brackets or bolts.

7. Prepare the New Pump: If the new pump is not pre-assembled, you may need to attach fittings, unions, or adapters to match your hot tub's plumbing. Ensure that you use the appropriate sealant or Teflon tape on threaded connections to prevent leaks.

8. Mount the New Pump: Position the new pump in the same location as the old one and secure it in place using the mounting brackets or bolts.

9. Reconnect Plumbing: Reconnect the plumbing to the new pump, ensuring that all connections are tight and secure. If your hot tub uses PVC plumbing, use PVC primer and cement to bond the connections properly.

10. Reconnect Electrical Wiring: Reconnect the electrical wiring to the new pump, following the notes or pictures you took earlier. Make sure all wires are properly connected and secure.

11. Turn On the Power: Restore power to the hot tub by switching on the circuit breaker or reconnecting the disconnect switch.

12. Test the Pump: Turn on the hot tub's pump to ensure that it's working correctly. Check for any signs of leaks or irregularities in the plumbing connections.

13. Refill the Hot Tub: Once you've confirmed that the new pump is functioning properly, refill the hot tub with water.

14. Check for Leaks: Inspect the plumbing connections for any leaks. If you find any, turn off the pump, drain the tub again, and reseal the connections as needed.

15. Monitor: Keep an eye on the pump and plumbing for the next few days to ensure everything is functioning correctly and that there are no further issues.

Remember that this is a general guideline, and the specific steps may vary based on your hot tub's design. If you're unsure or uncomfortable with any aspect of this process, please do get in touch, happy to help.

How do I know what size hot tub pump I have?

Determining the size of your hot tub pump is an important step when it comes to maintenance or replacement. To find out the size of your hot tub pump, follow these steps:

1. Check the Manual: The easiest way to determine the size of your hot tub pump is to consult the owner's manual or user documentation that came with your hot tub. The manual typically contains detailed information about the specifications and components of your hot tub, including the pump.

2. Look at the Pump Housing: If you don't have access to the manual or it doesn't provide the information you need, inspect the pump itself. Most hot tub pumps have a label or plate on the pump housing that displays essential details, including the pump's model number, manufacturer, and specifications. You can then send that to me or Google it.

3. Measure the Pump: If the label is missing or damaged, you can measure the pump's dimensions. Measure the diameter of the pump's wet end (the part where the water flows) and the length of the wet end. These measurements can help identify the size and capacity of the pump.

4. Consult the Manufacturer: If you can't find the information on the pump or in the manual, contact the hot tub manufacturer or a reputable dealer. Provide them with your hot tub's model and serial number, and they should be able to identify the correct pump size for your specific hot tub.

5. Online Research: You can also search online using the pump's model number or hot tub's make and model. Many manufacturers provide detailed information about their products on their websites, and you may find specifications for your pump model.

Once you have determined the size and specifications of your hot tub pump, you can proceed with maintenance, repairs, or replacement if necessary. Keep in mind that replacing a hot tub pump with the same size and capacity as the original is crucial to ensure proper water circulation and filtration in your hot tub. If you're unsure about any aspect of this process, get in touch, always happy to help.