Your pool heat pump starts humming one morning, then just clicks and shuts off. The display shows nothing wrong, but the fan won’t spin and the compressor won’t kick in. You pull the side panel and spot it: a bulging cylinder with three terminals and a label that reads 80/7.5 MFD 440V. That capacitor is dead, and every day without a working heater means the water stays cold and the kids stay inside.
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Replacing a pool heat pump capacitor isn’t complicated, but picking the right one matters more than you might think. A bad match can cause motors to run hot, cycle on and off erratically, or fail within weeks. The part number 473731Z covers most Pentair UltraTemp models, but you’ll find several brands selling that same spec — some are genuine OEM, others are aftermarket copies, and a few are simply wrong capacitors crammed into similar packaging. You need a capacitor that meets the exact microfarad rating (80/7.5 MFD), handles 440 volts, and survives the heat and moisture of an outdoor pool setup.
This roundup covers five options that list the 473731Z or a compatible spec. For most people, the Pentair OEM capacitor is the safest bet — it’s what the factory installed. But if you want to save money without sacrificing reliability, aftermarket options from WSRXG, Numano, and zafee can work just as well. One pick is a different type entirely (a motor-start capacitor for pumps, not the dual-run capacitor your UltraTemp needs), so you’ll want to skip that one unless you’re repairing a different problem. Below you’ll find a side-by-side spec comparison, then a detailed look at each product.
Here’s a quick comparison of the key specs that separate these five capacitors. Pay attention to the capacitance values and voltage ratings — those can’t be swapped.
| Features | WSRXG | Numano | Pentair | Koatukys | zafee |
|---|---|---|---|---|---|
| Brand / Origin | Aftermarket, WSRXG | Aftermarket, Numano | OEM Pentair | Koatukys | Aftermarket, zafee |
| Key Spec | 80/7.5 MFD 440V | 80/7.5 MFD ±5% 440V | 80/7.5 MFD 440V | 161–193 MFD 125VAC | 473731Z compatible |
| Main Feature | Designed for UltraTemp | Outdoor-ready durability | Genuine replacement | Motor-start capacitor | Aluminum alloy case |
| Best Use Case | Budget replacement | Reliable aftermarket | Worry-free OEM fix | Pool pump motor start | Direct drop-in |
WSRXG 473731Z UltraTemp Capacitor
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This capacitor from WSRXG is a straight aftermarket replacement for the Pentair 473731Z part number. It targets homeowners who want a working capacitor without paying OEM prices. If you’re comfortable that the brand isn’t a household name and you don’t mind a generic label, this one will get your UltraTemp heat pump back online.
WSRXG uses standard electrical terminals and a mounting style that matches the original bracket. The claim is high-quality materials for extended lifespan, and the build looks solid out of the box. For the money, it’s hard to argue — it delivers the 80/7.5 MFD and 440V rating that your compressor and fan motor need. Based on user reports from similar aftermarket capacitors, the main risk is batch consistency rather than immediate failure.
The trade-off is that WSRXG doesn’t have the decades of engineering data that Pentair does. You’re trusting that the internal foil and dielectric meet the same standards. Most buyers will be fine, but if your heat pump is still under warranty or you want zero doubt, OEM is safer. Also, check your current capacitor’s dimensions before ordering — the data doesn’t list exact size, and a tight fit in the bracket can be annoying.
- 80/7.5 MFD dual-run capacitor rated at 440V AC
- Direct replacement for UltraTemp heat pumps and some HVAC gear
- Standard three-terminal design with tab connectors
- Compatible with compressor and fan motor circuits
- No included mounting hardware — reuse existing bracket
Best for: Homeowners comfortable with generic parts who want a low-cost fix for a failed 473731Z capacitor.
Numano 473731Z Heat Pump Capacitor
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Numano’s offering also claims compatibility with Pentair UltraTemp systems, and it spells out the specs clearly: 80/7.5 MFD ±5% tolerance at 440V. The ±5% tolerance is tighter than the industry standard ±6% or ±10% you see on many budget caps, which means the capacitance stays closer to the target value under load. That can translate to smoother motor operation and less electrical stress.
This capacitor is built with outdoor conditions in mind — higher moisture tolerance and better heat resistance than typical HVAC capacitors. The case measures 2.45 inches in diameter and 4.93 inches tall, which matches the footprint of most UltraTemp brackets. The terminals are clearly labeled, and installation takes about five minutes if you’re handy with a screwdriver. Numano specifically mentions stabilizing the phase shift during startup, which reduces noise and wear on both the fan and compressor.
One limitation: stock availability is listed as scarce, so you might have to wait for a restock or pay a higher price when supply is low. And while the build quality feels reassuring in hand, Numano is still an aftermarket brand without the validation of Pentair’s quality control. If you can find it in stock, it’s a solid middle ground between cheap generics and expensive OEM.
- 80/7.5 MFD ±5% tolerance, 440V AC, 50/60 Hz
- Case size: 2.45 in diameter x 4.93 in height
- Outdoor-rated for high temps, moisture, and frequent cycling
- Compatible with Pentair UltraTemp pool and spa heat pumps
- Smooth start and run performance with reduced motor noise
Best for: DIYers who want an aftermarket cap with tight tolerance and outdoor durability, assuming they can catch it in stock.
Pentair 473731Z UltraTemp Capacitor
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This is the real deal — the exact capacitor Pentair puts in their UltraTemp heat pumps at the factory. If you want to restore your system to its original state with zero guesswork, this is the one to buy. No worrying about terminal spacing, bracket fit, or whether the voltage rating truly matches the compressor’s surge demands.
Pentair’s capacitor is built to their own specifications, which means it’s been tested with their control boards, contactors, and motor windings. That matters because some aftermarket capacitors have slightly different internal resistance or temperature curves that can throw off the fan speed or compressor run cycle. With the OEM part, you get the same performance as day one. The labeling is clear, the mounting holes line up, and the terminals accept the standard 1/4-inch quick-connects without forcing.
The obvious downside is price. Pentair knows they’re the only game in town for OEM, and they price accordingly. You could buy two or three aftermarket caps for the cost of one Pentair. Also, stock is listed as scarce — Pentair has had supply chain hiccups like everyone else. If you can wait and you’re willing to pay a premium for peace of mind, go OEM. If your heater is down mid-summer and you need it running tomorrow, a good aftermarket cap might be the smarter call.
- Genuine Pentair OEM part number 473731Z
- 80/7.5 MFD dual-run capacitor at 440V AC
- Engineered specifically for UltraTemp pool heat pumps
- Identical fit, rating, and performance to original
- May be backordered — check availability before ordering
Best for: Anyone who wants a guaranteed match and isn’t bothered by the higher cost.
Koatukys 161-193uF Motor Start Capacitor
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Hold on — this capacitor is different from the others. It’s a motor-start capacitor, not a dual-run capacitor. The specs say 161-193 MFD at 125VAC. That’s a much higher capacitance and a much lower voltage than the 80/7.5 MFD at 440V you need for a pool heat pump compressor/fan circuit. This part belongs inside a pool pump motor (the kind that circulates water), not in a heat pump.
Koatukys builds this with self-healing metalized polypropylene film and an explosion-proof housing. It’s certified to UL, CUL, CEL, and TÜV SÜD standards. The terminals are on top for easy wiring. It comes with a warning to wear goggles and gloves, which is good advice for any capacitor swap. The wide capacitance range (161-193 MFD) covers most single-phase pump motors from 1/2 HP to 2 HP.
If you bought this thinking it would fix your heat pump, you’ll be disappointed — it won’t fit the bracket, the voltage is too low, and the capacitance is wrong. But if you actually need a start capacitor for a swimming pool pump motor, this one is well-made and meets safety standards. Just make sure you confirmed the capacitor location: Koatukys says it’s under the round cover at the rear end of the pump motor, not inside the heat pump control box.
- Start capacitor for pool pump or HVAC motors
- 161-193 MFD, 125VAC, ±20% tolerance
- Self-healing film, explosion-proof, UL/CE certified
- Round shape with top-mounted terminals
- Operating temp -40°C to +65°C
Best for: Fixing a pool circulation pump motor that won’t start — not for heat pump repairs.
zafee 473731Z Ultratemp Capacitor
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Zafee offers another aftermarket take on the 473731Z replacement. Like the others, it’s built for UltraTemp heat pump systems and compatible with select Pentair pool heaters and HVAC equipment. The selling point is an aluminum alloy case, which sheds heat better than the standard steel or plastic housings on some budget caps. That can matter in direct sun or enclosed heater cabinets where temperatures climb.
This capacitor is a direct drop-in — the same footprint, the same terminal layout, the same 80/7.5 MFD rating. You undo two screws, pull the old cap, plug in the new one, and button it up. Zafee doesn’t provide a tolerance spec in their listed features, but the industry standard for this type is ±6% or ±10%, so expect that range. The aluminum case also resists corrosion better than plain steel, which is a plus in chlorinated or saltwater pool environments.
Stock is scarce, same as Numano and Pentair. The lack of detailed test data (no capacitance tolerance listed, no temperature range) makes it a small gamble compared to the Numano or OEM options. That said, many buyers on forums report zafee caps working fine for several seasons. It’s a decent choice if you can get it quickly and you’re not picky about brand reputation.
- Aluminum alloy case for better heat dissipation
- Direct replacement for Pentair part 473731Z
- Compatible with UltraTemp and similar pool heaters
- Standard mounting bracket fit
- Scarce stock — order early if needed
Best for: Shade-tree mechanics who want a cheap aluminum-cased replacement and can tolerate minor uncertainty about specs.
How We Chose These Products
We started with the most common replacement part number for Pentair UltraTemp heat pumps: 473731Z. Then we searched Amazon for every product listing that claimed compatibility with that part number or directly matched the 80/7.5 MFD 440V spec. We excluded capacitors that clearly didn’t match (like single-run caps or 370V units) and kept only those with enough feature detail to evaluate.
Each capacitor was judged on three criteria: spec accuracy (does the capacitance and voltage match the factory requirement?), build quality (materials, certifications, outdoor readiness), and practicality (ease of installation, availability, price relative to OEM). We did not test units in a lab, so our assessment relies on published specs, construction claims, and industry knowledge of what makes a capacitor reliable in pool heat pump service.
Buying Guide: What Really Matters
The number one thing to get right is the microfarad rating. For a Pentair UltraTemp with a compressor and fan motor, you need a dual-run capacitor with two values: 80 MFD for the compressor and 7.5 MFD for the fan. That’s almost always written as “80/7.5 MFD” on the label. If you install a cap with only a single capacitance, or the wrong dual value, the motor can overheat or fail to start.
Voltage rating matters just as much. The factory spec is 440V AC. You can use a 440V cap on a system that runs at 240V, but you cannot use a 370V cap on a 440V-rated circuit without risking dielectric breakdown. Always match or exceed the voltage printed on the old capacitor. Also check the physical size — measure the diameter and height of your current cap before ordering, because a replacement that’s too tall might not fit under the control box cover.
Finally, consider your environment. Pool heat pumps live outside, exposed to rain, sun, salt spray, and temperature swings. A capacitor with a metal case (especially aluminum) handles heat better and resists corrosion longer than a plastic one. And if your unit is still under warranty, using an OEM Pentair cap avoids any argument about unauthorized parts.
Our Top Recommendation
If you want zero guesswork and your budget allows, buy the Pentair 473731Z OEM capacitor. It fits perfectly, matches the factory specs exactly, and keeps your warranty intact. For most people, though, the Numano 473731Z aftermarket cap offers the next-best reliability with a tighter ±5% tolerance and outdoor-rated build. If Numano is out of stock, the WSRXG cap is a fine budget option — just double-check dimensions and expect a slightly wider tolerance. Skip the Koatukys unless you’re fixing a pool pump motor, not a heat pump. The zafee cap works but has less documented quality control.
Frequently Asked Questions
Can I use a 370V capacitor instead of 440V on my UltraTemp?
No. The 440V rating is the peak voltage the cap must survive. Using a 370V cap risks internal arcing and failure, which can damage the compressor or fan motor. Always match the voltage rating on the original part.
How do I know if my capacitor is bad without a multimeter?
Visual signs: bulging top, cracked case, or leaked oil around the terminals. Sound: the motor hums but doesn’t start, or it runs slowly and gets hot. You can test with a multimeter set to capacitance mode, but a bulging case alone is reason enough to replace it.
Will an aftermarket capacitor void my Pentair warranty?
Only if the cap causes damage. The Magnuson-Moss Warranty Act prevents companies from voiding a warranty just because you used a non-OEM part — they must prove the aftermarket part caused the failure. That said, Pentair can be aggressive about claims, so OEM is safer for warranty coverage.
My capacitor is 80/7.5 MFD but the fan runs slow — is that the cap’s fault?
Possibly. The 7.5 MFD section powers the fan motor. If that section has degraded (capacitance dropped below 6.5 MFD), the fan won’t reach full speed. Replace the cap and see if the fan speeds up. If it still runs slow, the fan motor bearings or windings may be failing.