💪 Waterway Spa-Flo II Pump 3420610-S1Z — 1.5 HP 2-Speed 115V 48-Frame

High-flow spa pump engineered for direct Aqua-Flo FMHP replacement and 1-1/2″ plumbing systems

📋 Product Overview

The Waterway Spa-Flo II (Part No. 3420610-S1Z) is a 1.5 HP, 2-speed, 48-frame jet pump designed for superior and efficient performance in spa and hot tub applications. Manufactured in the USA by Waterway Plastics of Oxnard, California, this pump features high flow rate performance optimized for faster filtration cycles and powerful hydrotherapy jets — delivering 3,450 RPM on high speed and 1,725 RPM on low speed.

Engineered as a direct replacement for the Aqua-Flo FMHP and other popular 1-1/2″ plumbing spa pumps, the Spa-Flo II combines a proven 48-frame design with Waterway’s premium seal technology: silicone carbide faces, Viton bellows, and 316 stainless steel casing for exceptional resistance to chlorine, bromine, and salt water systems. The side-discharge wet end rotates for flexible plumbing configurations, and at just 16″ overall length and approximately 29.5 lbs, it fits most existing pump compartments. With 1-1/2″ MBT intake and discharge connections (~2-3/8″ thread OD) and broad cross-compatibility with dozens of OEM part numbers, the Spa-Flo II is an ideal choice for both new installations and spa pump replacements. Cord and unions are sold separately.

✨ Key Features

• ✅ 1.5 HP / 2-Speed Operation — High speed (3,450 RPM) for jets; low speed (1,725 RPM) for energy-efficient filtration
• ✅ 115V / 60Hz — Standard US voltage with automatic overload protection
• ✅ Direct Aqua-Flo FMHP Replacement — Drop-in replacement for the most popular 1-1/2″ spa pump on the market
• ✅ 1-1/2″ MBT Intake and Side Discharge — Thread OD approximately 2-3/8″ for standard 1-1/2″ plumbing
• ✅ Premium Viton Seal — Silicone carbide faces, Viton bellows, 316 stainless steel casing for maximum chemical resistance
• ✅ 48-Frame Proven Design — Industry-standard mounting for broad compatibility
• ✅ Rotatable Wet End — Side discharge orientation can be rotated for flexible plumbing options
• ✅ High Flow Rate Performance — Engineered for faster filtration cycles
• ✅ Thermally Protected Motor — Automatic overload protection extends motor life
• ✅ Made in the USA — Designed, engineered, and manufactured by Waterway Plastics in Oxnard, California
• ✅ Can Be Wired Single or Dual Speed — Easily configured for 1-speed or 2-speed spa control systems

🔩 Technical Specifications

Specification	Value
Part Number	3420610-S1Z
Alternate Part Numbers	3420610-0Z, 3420610-1Z, 3420610-S0Z, 3420610-1E, 3420410-S1Z, CP-15-2N11CD, CP-15-2N11MD
Manufacturer	Waterway Plastics (Oxnard, CA, USA)
Pump Series	Spa-Flo II — 48-Frame
Pump Type	Jet Pump — Side Discharge
Motor Power	1.5 HP
Speed Settings	2-Speed (High and Low)
High Speed RPM	3,450
Low Speed RPM	1,725
Voltage	115V
Frequency	60 Hz
Amperage (High Speed)	See amperage note below
Amperage (Low Speed)	See amperage note below
Frame Type	48Y (Thru-Bolt)
Discharge Port Size	1-1/2″ MBT (Male Buttress Thread)
Suction Port Size	1-1/2″ MBT (Male Buttress Thread)
Discharge Location	Side — Rotatable
Suction Location	Center (front face)
Thread Outer Diameter	Approximately 2-3/8″ (2.375″)
Overall Length	16″
Height	8.19″
Weight	Approximately 29.5 lbs
Seal Type	Viton — Silicone carbide faces, Viton bellows, 316SS casing
Thermal Protection	Yes — Automatic overload protection
Unions Included	No — Sold separately
Cord Included	No — Cord not included
Country of Manufacture	USA
Warranty	1 Year (Manufacturer)

⚠️ Amperage Note — Important: Waterway has transitioned to more energy-efficient motors over time, and the amperage on this pump varies depending on which motor brand is installed:

Motor Version	High Speed	Low Speed	Source
Older motors (A.O. Smith)	16.4A	4.4A	Parts4Tubs, Amazon, Newegg, SpaPartsProShop
Newer motors (US Motors/other)	13.3A	4.1A	HotTubOutpost (confirmed by Waterway)
Some motor variants	13.5A	4.7A	SpaParts, pool-spa-supplies

HotTubOutpost confirms from Waterway: the newer 13.3A motors deliver the same performance as the older 16.4A motors — they are simply more energy efficient. Waterway reserves the right to change motor brands without notice. Always check the motor nameplate on your specific pump and size your circuit for the highest possible amperage rating.

⚡ Electrical Requirements

Electrical Spec	Requirement
Supply Voltage	115V
Frequency	60 Hz
Phase	Single
Full Load Amps (High Speed)	Up to 16.4A (varies by motor — see note above)
Full Load Amps (Low Speed)	4.1A to 4.4A (varies by motor — see note above)
Wiring	Per motor nameplate wiring diagram

⚠️ IMPORTANT:

All electrical work must be performed by a licensed electrician in accordance with the National Electrical Code (NEC) and all applicable local and state building codes.

Hot tubs and spas require GFCI (Ground Fault Circuit Interrupter) protection. The pump must be supplied through a GFCI device with rated residual operating current not exceeding 30mA.

A dedicated circuit is required — do not share with other appliances.

Ground the motor prior to connecting electrical power. Applied voltage must be within 10% of the nameplate rating.

For 2-speed models: Do not wire both speeds to run simultaneously. When removing the power cord from an existing pump, mark your wires for “common,” “high speed,” and “low speed.” The connection diagram is on the motor nameplate.

🔗 Compatibility Guide

This Pump:

• 📐 Frame: 48Y (Thru-Bolt)
• 📐 Intake: 1-1/2″ MBT — Center (front face)
• 📐 Discharge: 1-1/2″ MBT — Side (rotatable)
• 📐 Thread OD: ~2-3/8″ (2.375″)

Direct Replacement for Aqua-Flo FMHP:

The Waterway Spa-Flo II is specifically designed as a direct replacement for the Aqua-Flo/Gecko FMHP series, one of the most widely used 1-1/2″ spa pumps in the industry.

Aqua-Flo / Gecko Cross-Reference Part Numbers:

Part Number	Notes
02115000-1010	Aqua-Flo FMHP — primary cross-reference
02115000	Aqua-Flo FMHP base part number
02115000-1040	Aqua-Flo FMHP variant
02115000-2010	Aqua-Flo FMHP variant
02110000-1010	Aqua-Flo cross-reference
02010422-5	Aqua-Flo cross-reference
02115851	Aqua-Flo cross-reference
03115452-2	Aqua-Flo cross-reference
1431501-01	Aqua-Flo cross-reference
1431501-03	Aqua-Flo cross-reference
93495111	Aqua-Flo cross-reference
FMHP551521	Aqua-Flo FMHP model designation
FMHP-551021	Aqua-Flo FMHP model designation
GK020100001010	Gecko cross-reference

Other Waterway Cross-Reference Part Numbers:

Part Number	Notes
3420610-0Z	Waterway Spa-Flo — without “S” prefix
3420610-1Z	Waterway Spa-Flo variant
3420610-S0Z	Waterway Spa-Flo II variant
3420410-S1Z	Waterway Spa-Flo single-speed variant
34206100Z	Alternate format
WW342061015	Alternate format

Additional Cross-Reference Part Numbers:

Part Number	Notes
1-00-0208	Cross-reference
34-402-5002	Cross-reference
5030-501	Cross-reference
15-350-2292	Cross-reference
34-270-3644	Cross-reference

⚠️ Union Compatibility Warning: Unions are NOT included. Different pump brands use different union thread sizes and styles. If you are replacing a non-Waterway pump, you will most likely need to install new unions compatible with the Waterway 1-1/2″ MBT thread. Some brands (such as Hayward, Jacuzzi, or Sta-Rite) may use non-standard fittings with different dimensions.

🛠️ Installation Requirements

Mounting:

Requirement	Specification
Mounting Position	Horizontal — Place on level surface
Location	Below water surface (flooded suction)
Area	Clear of direct water with adequate floor drainage
Protection	Protect from excessive moisture
Restriction	Do not install within an outer enclosure or beneath the skirt of a spa unless so marked

Plumbing:

Connection	Size
Suction (Intake)	1-1/2″ MBT — Center (front face)
Discharge	1-1/2″ MBT — Side (rotatable)
Thread OD	Approximately 2-3/8″ (2.375″)

Installation Notes:

⚠️ Wet end can be rotated by loosening the motor thru-bolts and turning the pump head to match your existing plumbing

⚠️ Install shut-off valves on both the inlet and outlet for future maintenance

⚠️ Do not use pipe dope — use only Teflon tape or other sealing compounds approved for plastic. Some pipe dopes cause stress cracking of plastic parts

⚠️ Hand tighten unions only — do not overtighten

⚠️ Pressure testing should not exceed 40 PSI — ensure all air is removed during the pressure test

⚠️ Ensure proper grounding and bonding per NEC requirements

⚠️ GFCI protection is required by code for all hot tub and spa installations

🔄 Maintenance Guide

Routine Maintenance:

Task	Frequency	Notes
Check for leaks	Monthly	Around seal, unions, and connections
Inspect unions and fittings	Monthly	Hand tighten only if needed
Clean strainer/filter	As needed	Remove debris to maintain flow
Check amperage	Annually	Should be within 10% of nameplate rating
Inspect motor vents	Quarterly	Keep clear of debris for cooling
Check mounting	Quarterly	Ensure pump is secure on level surface

Warning Signs — Replace Pump If:

• Unusual noise (grinding, screeching, bearing noise)
• Water leaking from shaft seal
• Motor trips breaker repeatedly
• Reduced water flow through jets
• Motor overheating or thermal protector tripping repeatedly
• Motor hums but won’t start (possible capacitor or winding switch failure)

Spa-Flo Wet End Replacement Parts (Waterway OEM — from Waterway Parts Catalog PDF):

Part Number	Description
319-3100B	Pump Seal Kit (Viton)
310-4070	Spa Flo Impeller Assembly — 1.5 HP
310-4060	Spa Flo Impeller Assembly — 1 HP
310-4090	Spa Flo Impeller Assembly — 2 HP
315-1060	Volute
311-1060	Faceplate
805-0248	Volute O-Ring
819-1110	Screw #8-32 (8 required)
310-7830	Complete Wet End — Spa-Flo II 1.5 HP

Motor Cross-Reference (for motor-only replacement):

Part Number	Notes
BN50	Primary motor model
RB804	Cross-reference
5KCP39SN4457X	GE motor cross-reference
EZBN50	Cross-reference

🎯 Ideal Applications

Application	Suitability	Notes
♨️ Hot tub jet pump (1-1/2″ plumbing)	✅ Yes — Primary application	Designed for 1-1/2″ intake and discharge spa systems
♨️ Aqua-Flo FMHP replacement	✅ Yes — Direct drop-in	Verified direct replacement with matching dimensions and connections
♨️ Spa filtration/circulation	✅ Yes	Low speed provides energy-efficient filtration at 1,725 RPM
♨️ Plug-and-play spa (115V)	✅ Yes	Suitable for 115V systems with 1-1/2″ plumbing
♨️ Salt water spa systems	✅ Yes	Viton seal with 316SS casing resists salt corrosion
♨️ Spas with 2″ plumbing	❌ Not compatible	Use Waterway Executive or EX2 series for 2″ plumbing systems

❓ Frequently Asked Questions

Q: What horsepower is this pump? A: 1.5 HP, 2-speed. High speed at 3,450 RPM for jets, low speed at 1,725 RPM for filtration.

Q: Is this a direct replacement for the Aqua-Flo FMHP? A: Yes. The Waterway Spa-Flo II is specifically designed as a direct drop-in replacement for the Aqua-Flo/Gecko FMHP series with matching 1-1/2″ MBT connections and 48-frame motor. Verified cross-reference part numbers include 02115000-1010 and FMHP551521.

Q: What is the difference between the Spa-Flo II and the Executive? A: The primary difference is port size. The Spa-Flo II has 1-1/2″ intake and discharge connections (thread OD ~2-3/8″), while the Executive has 2″ connections (thread OD ~3″ to 3-1/16″). The Executive also has a larger 6-1/2″ diameter wet end for higher head pressure and carries a longer warranty (2yr motor / 3yr wet end vs. 1yr for Spa-Flo II). Choose based on your existing plumbing size.

Q: Why do different sources list different amperages? A: Waterway has transitioned to more efficient motors over time. Older units with A.O. Smith motors draw 16.4A/4.4A, while newer units with US Motors or other brands draw 13.3A/4.1A. HotTubOutpost confirms from Waterway that the newer motors deliver identical performance with lower energy consumption. Always check the motor nameplate on your specific pump. Size your circuit for the highest possible rating (16.4A).

Q: What voltage does this pump require? A: 115V / 60Hz. Do not use on 230V circuits. All electrical installation must be performed by a licensed electrician.

Q: Are unions included? A: No. Unions are sold separately. Different pump brands use different union thread sizes, so if replacing a non-Waterway pump, you will likely need new unions. Some brands (Hayward, Jacuzzi, Sta-Rite) use non-standard fittings.

Q: Is a pump cord included? A: No. The cord is sold separately.

Q: What size are the ports? A: Both intake and discharge are 1-1/2″ MBT. The outer thread diameter is approximately 2-3/8″ (2.375″). This is NOT the same as the 2″ connections (~3″ thread OD) on the Executive or EX2 series.

Q: Can I use this pump if my existing pump has 2″ connections? A: No. If your existing pump has 2″ intake and discharge (approximately 3″ thread OD), you need the Waterway Executive (3420610-1A) or EX2 (3420610-1U) series instead. The Spa-Flo II’s 1-1/2″ connections are not compatible with 2″ plumbing.

Q: What seal does this pump use? A: Waterway pump seal kit 319-3100B — a premium Viton shaft seal with silicone carbide faces and 316 stainless steel casing. Replace at first sign of leakage.

Q: What warranty is included? A: 1-year manufacturer warranty from Waterway Plastics. Contact Parts4Tubs for full warranty terms.

Q: Do I need a GFCI breaker? A: Yes. GFCI protection is required by the National Electrical Code (NEC) for all hot tub and spa installations. Waterway specifies a GFCI device with rated residual operating current not exceeding 30mA.

📥 Downloads & Resources

📄 48-Frame Center & Side Discharge Pumps Installation Manual (PDF) — Installation instructions, wiring guidance, troubleshooting chart, and safety warnings for all Waterway 48-frame pumps including Spa-Flo II (Document 810-0003)

🏆 Why Choose the Waterway Spa-Flo II

• ✅ Made in the USA — Designed, engineered, and manufactured by Waterway Plastics in Oxnard, California
• ✅ Direct Aqua-Flo FMHP replacement — Verified drop-in compatibility with the industry’s most popular 1-1/2″ spa pump
• ✅ Premium Viton seal — Silicone carbide faces with 316 stainless steel casing for maximum chemical resistance
• ✅ High flow rate performance — Engineered for faster filtration cycles and powerful jets
• ✅ Thermally protected motor — Automatic overload protection extends motor life
• ✅ Proven 48-frame design — Industry-standard mounting for maximum compatibility
• ✅ 2-speed energy savings — Low speed filtration dramatically reduces electricity costs

🤝 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
• ✅ Replacement seals, impellers, wet ends, and parts available
• ✅ Dedicated customer service team

⭐ Summary

The Waterway Spa-Flo II (3420610-S1Z) is a USA-made, 1.5 HP, 2-speed jet pump designed for 1-1/2″ plumbing spa systems. Operating at 115V/60Hz with a proven 48-frame design, it serves as a direct drop-in replacement for the Aqua-Flo FMHP — the industry’s most widely used 1-1/2″ spa pump. Premium Viton seal technology with silicone carbide faces and 316 stainless steel casing ensures long-lasting chemical resistance. At 16″ overall length and approximately 29.5 lbs with rotatable side discharge, it fits most existing installations. Order today from Parts4Tubs for fast US shipping and expert compatibility 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: 597 Min: 1 Step: 1 Add to cart
	Magic Plastics Union 0602-20 (2″ Pump Union) | 2″S x 2″FBT w/ O-Ring Union, Pump, Magic, 2"S x 2"FBT (Industry Standard) w/ O-Ring	$8.00 Max: 575 Min: 1 Step: 1 Add to cart
	Waterway Union 400-6010 | 2-1/2″ Union Nut with 2-1/2″ Slip tailpiece and o-ring (2.5″ union) Union, Pump, Waterway, 2-1/2"FBT x 2-1/2"S	$14.77 Max: 83 Min: 1 Step: 1 Add to cart
	1 Speed Pump / Blower / AMP Cord | 21086 Amp Plug, Pump, 1-Speed, 14/3, 4-Pin, 5' Cord, White	$24.71 Max: 356 Min: 1 Step: 1 Add to cart
	Balboa Amp Plug 21087 (For 2 Speed Pumps) Amp Plug, Pump 1 (2-Speed) 14/4, 72" Long, White	$31.72 Max: 153 Min: 1 Step: 1 Add to cart

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.