Hot Tub Pump Capacitors: How to Test and Replace Start and Run Capacitors

Updated September 2026. I’ve rewritten this guide to explain properly how start and run capacitors work, corrected the testing method (the original told you to use the ohms setting, which won’t tell you much), and added safer discharge steps and a troubleshooting table.

Your hot tub pump hums when you press the jets button, but nothing happens. Before you buy a new pump, check the capacitor. It’s a cheap part, it wears out over time, and swapping it is one of the easiest repairs you can do on a hot tub.

This guide covers what a capacitor does, the two types used on hot tub pumps, how to tell if one has failed, how to test it safely, and how to replace it.

What is a capacitor?

A capacitor is an electrical component that stores charge. Inside are two conductive layers separated by an insulator. Capacitance is measured in farads. One farad is a very large amount, so the capacitors on pump motors are rated in microfarads (µF, sometimes written MFD), which are millionths of a farad.

In the original version of this post I said to think of a capacitor like a battery, like the one that starts your car. That’s handy for one thing: remembering that it can hold a charge after the power’s off. But it isn’t how it works in a pump. A capacitor doesn’t power the motor. It shifts the timing of the current in the motor’s second winding, which creates the rotating magnetic field that gets a single-phase motor turning in the right direction.

Start and run capacitors: what’s the difference?

Hot tub pumps run on single-phase power, and a single-phase motor can’t start itself. It needs help from a second winding and a capacitor. Depending on the motor, you’ll find one or both of these:

	Start capacitor	Run capacitor
Job	Extra torque to get the motor spinning	Keeps the motor running smoothly and efficiently
When it’s in circuit	Only at start-up; a switch drops it out at around 2/3 to 3/4 speed	All the time the pump is running
Typical rating	50–400µF, 125 or 250V	15–50µF, 370V
Usually looks like	Black plastic case	Metal or plastic can
Failure signs	Sluggish start or hum with no start; may leak or vent	High current, overheating and tripping the motor’s thermal cut-out; ends may bulge

Typical ratings and failure signs from INYO Pools’ capacitor guide. Your capacitor may be outside these ranges, so always go by its label.

A correction: when I first wrote this, I said every hot tub pump has both a start and a run capacitor, and I described the start capacitor as powering a “starter motor”. That wasn’t right. There’s no separate starter motor, and many hot tub pumps (particularly smaller ones) use a single run capacitor that does both jobs. Others, such as Waterway’s Executive pumps, use both a start and a run capacitor. Take the cover off and see what you’ve got.

Values vary a lot between pumps. For example, the LX WP200 and LP200 pumps common on UK and European tubs take a 30µF capacitor.

Where do I find the capacitor?

It depends on the pump, but it’s always under a cover on the motor. On Waterway and LX pumps, it’s usually on top of the motor in a small sealed box, like the one below. On other pumps, look for a removable cover (sometimes called the “doghouse”) on the top or the back of the motor.

Be careful. Turn off the power at the isolator before you remove any cover. Even with the power off, a capacitor can hold a charge, so treat it as live until you’ve discharged it (see below). Never bridge the terminals with your fingers or a screwdriver.

Signs your pump capacitor has failed

Capacitors are a consumable part. Age and heat in the equipment bay wear them out, so at some point you’re going to need to change one. Signs to look for:

• The pump hums but won’t turn. You press jets, hear the relay in the spa pack click, and the motor hums without spinning. This is the classic symptom.
• A sluggish start. The motor takes a second or two to get going, or sometimes doesn’t start at all.
• It starts on one speed but not the other. On a two-speed pump, this points to a capacitor or start circuit problem. Originally I said this definitely means the start capacitor. It’s a good clue, but test the capacitor to be sure.
• It runs noisy and lumpy, gets hot or trips its thermal cut-out. This can point to a weak run capacitor.
• The capacitor looks swollen, bulging, cracked or leaking. Replace it.

Not every hum is a capacitor. A seized pump does exactly the same thing. That could be worn bearings, debris jammed in the impeller, or a pump that’s sat unused over winter. With the power off, check whether the motor shaft turns freely by hand (some motors have a slot for a screwdriver in the end of the shaft). If it’s stiff or gritty, a new capacitor won’t fix it. If your pump is loud as well, see Noisy hot tub pump?

How to test a hot tub pump capacitor

Another correction: the original version of this guide told you to set your multimeter to the lowest ohms setting and replace the capacitor if it read 0. That’s not a reliable test. Most modern multimeters have a capacitance setting (marked µF or with a capacitor symbol), and that’s what you want.

1. Isolate the power to the hot tub at the isolator, and check with your meter that the supply is dead.
2. Take a photo of the wiring so you know which wire goes where.
3. Discharge the capacitor. A motor controls guide from Open Oregon recommends holding a 20,000Ω, 2–5 watt resistor across the terminals for 20–40 seconds. Use insulated leads, and don’t short it with a screwdriver.
4. Disconnect the capacitor from the motor so you’re only measuring the capacitor.
5. Set your meter to capacitance, put a lead on each terminal and wait for the reading to settle.
6. Compare it with the rating on the label. A healthy capacitor reads within its printed tolerance, typically within ±10%. A reading well below that, zero or “OL” means it needs replacing.

If your meter doesn’t have a capacitance setting, a new capacitor is cheap enough that many people simply swap it and see if the pump starts.

How to replace a hot tub pump capacitor

1. Isolate the power and confirm it’s off.
2. Remove the capacitor cover on the motor.
3. Photograph the wiring and discharge the old capacitor as above.
4. Unclip or unscrew the bracket holding the capacitor, if there is one.
5. Pull off the spade connectors one at a time, keeping hold of the wires so they don’t drop inside the motor. Don’t let the two wires touch each other.
6. Fit the new capacitor to the same terminals, refit the bracket and cover, restore power and test.

Choosing the right replacement

• Match the µF rating. Use the same value as the old one wherever you can. Start capacitors are often labelled with a range (for example 88–108µF), so match that range. INYO’s advice is never to fit a lower-rated capacitor, and if the exact size isn’t available, one step higher is acceptable.
• Match or exceed the voltage. A 370V capacitor can be replaced by a 440V one of the same µF, but never by a lower voltage.
• Check the physical size and terminals so it fits under the cover.

Replacing a capacitor can save you the cost of a whole pump, and for most DIYers it really is about a 15-minute job. If you’re not comfortable working with electrics, though, get a qualified electrician or spa technician to do it.

New capacitor and it still won’t start?

What you see	Likely cause
Hums, and the shaft is stiff or gritty by hand	Seized bearings or a jammed impeller
No hum, no click	No power to the pump: spa pack relay, fuse, wiring or topside control
Clicks, but no hum	Loose or burnt connection, or a failed motor winding
Runs, but trips the RCD/GFCI	Water in the motor or a fault to earth. See why your hot tub trips the breaker
Runs, but little or no water moves	Air lock, closed valve or a blocked impeller. See how to deal with a hot tub air lock

If the motor itself is on its way out, read Should I repair or replace my hot tub pump? Sometimes it’s only the wet end that needs replacing (see my guide to pump wet ends). For everything else pump-related, including speeds and wiring, see The ultimate guide to all things hot tub pump. If you’re buying a replacement pump, check the union sizes first and make sure it’s the right size for your tub. If there’s no power reaching the pump at all, Hot tub wiring explained is a good place to start.

Need a capacitor or a new pump?

For capacitors, pumps and wet ends, head to parts4tubs.co.uk in the UK or parts4tubs.com in the USA. Send a photo of your pump label and your capacitor, and we’ll help you match it.

FAQs

How do I know if my hot tub pump capacitor is bad?

The pump hums but won’t spin, starts sluggishly, or the capacitor is visibly swollen or leaking. Confirm it by testing on a meter’s capacitance setting.

Can I replace a capacitor with a higher µF one?

Match the µF wherever you can. If the exact size isn’t available, one step higher is generally acceptable, but never go lower. A higher voltage rating with the same µF is fine.

Why does my hot tub pump hum but not turn on?

Usually a failed capacitor or a seized pump. Check that the shaft turns freely with the power off, then test the capacitor.

How much does a hot tub pump capacitor cost?

Usually a small fraction of the cost of a new pump. That’s why it’s always worth checking the capacitor first.

Is it safe to replace a pump capacitor myself?

Yes, if you isolate the power and discharge the capacitor before touching it. If you’re not confident with electrics, call a professional.

Got a pump that’s still humming? Drop a comment below with the make and model. I read them all.

Cheers,
Andi

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Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi