6 Signs a Pool Pump Capacitor Is Bad (and how to test)

Each day, when you turn on your pool pump, the pool pump run capacitor is at play. When yours starts to go faulty, it can affect the pool pump and even prevent it from turning on or starting. What are some signs the pool pump capacitor is in bad shape?

Here’s how to tell if the pool pump start (or run) capacitor has gone bad:

  • Humming pump but no startup
  • The pump is intermittently starting
  • The impeller is fine but the pump is not working
  • The pump shaft and bearings are fine but the pump is not working
  • The capacitor has bulges or smells
  • Noisy pump

In today’s extensive guide, we’ll walk you through the above signs so you can diagnose any potential issues with your pool pump capacitor. We’ll also discuss what causes pool pump capacitor failure, what you’ll spend to replace yours, and how to do it yourself.

Let’s get started!

Pool pump motor capacitors
Pool pump motor capacitors | Credit: Chris Dill of Dill’s Repairs

What Do Pool Pump Capacitors Do?

Before we get into all that, let’s talk a little more about what a pool pump capacitor is and what it does.

There are two types of pool pump capacitors:

  • Start capacitor
  • Run capacitor

Some pumps only have a start capacitor whilst others have both a start and a run capacitor.

Start Capacitors

The best way to describe a pool pump start capacitor is to liken it to the battery in your car.

You might know if you’ve ever accidentally drained the battery that once your car battery is dead, you can’t start your vehicle until you get a jump.

Well, the pool pump capacitor gives the pump motor the initial jolt or boost in energy it needs to get started. Once the pump motor starts turning, the start capacitor no longer plays a role.

Run Capacitor

This is where the run capacitor now comes into play. When the motor is running, the run capacitor provides a constant source of power to the copper windings in the motor. Without this capacitor, the motor speed might be erratic or noisy.

What Do Pool Pump Capacitors Look Like?

The average pool pump capacitor measures three to four inches and is cylindrical and long. Depending on the type of motor you have, the pump might run a single capacitor, or up to two.

The first capacitor would be the start capacitor while the second is the run capacitor.

You can generally find your pool pump capacitor(s) on the pool pump, at the side or top of the pump. The capacitor will be a bump or hump that’s held in place with plastic housing.

You can either unscrew the housing or pop it off. Within the cylinder store in the housing will be the capacitor.

Related Reading: Are Variable Speed Pumps Better Than Single Speed or 2 Speed Pumps?

5 Signs Your Pool Pump Capacitor Is Bad

Your pool pump capacitor can run for thousands of on-off cycles but it will not last forever. Before the capacitor goes on the fritz completely, you’ll notice signs that the capacitor is going bad.

Per the intro, here are five of the most overt signs to be on the lookout for.

1. Pump Motor Hums or Buzzes But Doesn’t Start

When you power on your pool pump, do you hear an odd humming sound? That sound isn’t coming from the pump itself. It’s the motor trying to start turning, but it doesn’t quite have enough power to turn.

Sometimes, the sound is more like a buzzing, but neither is good. Although it’s possible the bearings are seized or there is a blockage in the impeller, if your pump is a few years old, it’s likely to be the start capacitor.

It will need replacing.

2. Pump Motor  Starts But Turns Off Intermittently

Perhaps you can get your pool pump to turn on…well, for now, at least. After a bit of time spent running, the motor powers itself off.

If the circuit breaker isn’t tripping, this is a sign that the start or run capacitor needs replacing.

3. The Impeller Has No Blockages But the Pump Still Won’t Run

Your pool pump has an impeller that sits in the impeller housing behind a pump basket. The basket catches debris and prevents it from entering the impeller housing.

Like any pool basket, the pump basket isn’t perfect. Very fine debris can pass through the pump basket and reach the impeller housing, eventually causing a blockage in the impeller. You could also have a crack or hole in the pump basket.

If the impeller is blocked and your pool pump won’t start or hum, that’s one thing. Yet what if the impeller is fine? Then the capacitor could be on its way out.

4. The Pump Shaft or Bearings Are Good But the Pump Won’t Run

The pool pump also features a shaft that creates a seal and some bearings to keep it turning smoothly.  If the shaft is misshapen or damaged in some way, the pump will not operate properly. Bearings on the way out tend to make grinding or squealing noises. Both of these could impede the pump and stop it from turning.

You can check this by disconnecting the power and manually turning the pump shaft. If it’s difficult to turn, the bearings could be the cause.

If the pump shaft and bearings are good, then it could be the capacitor to blame.

5. Circuit Breaker Trips

A faulty pool pump capacitor can cause the pump circuit breaker to trip. A bad capacitor can mean the motor won’t start. If the motor doesn’t turn, then it can draw a high amount of current which can overload the circuit. As a result of an overloaded circuit, the pump circuit breaker will trip.

6. The Capacitor Smells and/or Is Misshapen

The last but best indication that something is wrong with your pool pump capacitor is twofold.

For one, if you notice a strange scent emanating from your pool pump motor and you’re ruled out by other sources (such as pool chemicals or local wildlife), it could be the capacitor. The capacitor can give off a smell as it begins to die.

You might also notice, once you find and look at the pool pump capacitor, that it’s misshape. It almost looks like it’s bulging. And in some cases, it can fail completely and be split open. This is a definite sign that the capacitor is on the way out or has failed.

What Causes a Pool Pump Capacitor to Fail?

You’ve deduced that your pool pump capacitor is on borrowed time. What has caused this to happen? Let’s take a closer look.

Heat

It’s not necessarily overheating that can burn out a pool pump capacitor but the heat in general.

Given that you use your pool in the summertime when it’s hottest, it’s inevitable that the capacitor is going to be exposed to heat.

If you live in a temperature region such as Florida or Australia and your pool is open all year long, your capacitor might last even less time than a pool owner’s who doesn’t use their pool for more than half the year.

In addition to this, poor ventilating to the capacitor can cause premature failure. As an ex-electronics technician, I’ve seen hundreds of capacitors, especially cheap ones, succumb to the heat.

Age

As with all things, age will cause your pool pump capacitor to stop working eventually. The capacitor, by the time it’s a few years old, has already undergone possibly thousands of starts and stops.

Every electronic component has a limited life, so one of these days, the pool pump motor capacitors will stop working.

Incorrect Voltage Rating

This is likely to be the least likely cause but it’s possible that someone has installed the wrong value capacitor.

Pool pump capacitors are only built to handle a certain amount of voltage. For example, common voltage ratings are 250V or 370V. You can maybe surpass that recommended voltage by a little. Going too much higher though can fry the capacitor.

If your pool motor required a 370V capacitor and a 250V cap was installed, the capacitor is likely to fail quickly. If not immediately.

Faulty and blown pool pump motor start capacitor.
Faulty and blown pool pump motor start capacitor | Credit: Chris Dill of Dill’s Repairs

Related Reading: 20 Reasons Why Pool Pumps Lose Pressure (and what to do)

How to Test a Pool Pump Capacitor

A multimeter is your best tool for gauging whether your pool pump capacitor is past the point of saving. Saying that they are not always accurate.

Here’s how to use a multimeter to test your pool pump capacitors:

Step 1 – Remove the Housing From the Motor to Access the Capacitor

We talked in the first section about where to find your pool pump capacitor. Following those instructions, access the capacitor now and remove any housing or covering.

Step 2 – Discharge the Capacitor

Capacitors can hold an electric charge for many days after their last use. To avoid giving yourself a nasty zap or shock, you need to discharge it. You can do it by shorting it out.

The best way to do that is to take an insulated screwdriver and place it over the capacitor’s leads.

Do make sure that you have eye and hand protection and get a good deal away while the pool pump capacitor is shorting out. Depending on how much charge is in the capacitor, it may make a loud bang and spark. This is normal.

Step 3 – Detach the Capacitor Leads

Once the capacitor has shorted out, measure the voltage across it to make sure it has been fully discharged. If it has, take off the leads. You may want to take a picture of the leads so you know how they go back together.

Step 4 – Test the Capacitor

Now it’s time to test the pool pump capacitor. We’re going to do two tests:

Test One: Resistance

Select on your multimeter, ohms.

Then connect the probe of the multimeter to the terminal of the capacitor, one probe each.

You’ll notice the numbers or meter needle begins moving up quickly and goes back to zero. Well, unless the capacitor is completely dead, that is. Then it may be dead.

This test is better done on an analog meter. A digital meter may not display any reading.

Test Two: Capacitance

Set your meter to Ohms. Now take a note of the capacitance on the side of the capacitor. It will be a number like 149uF. This is the capacitance.

Put your meter probes on the capacitor terminals. Note the capacitance. Then reverse the probes putting them the other way around.

The capacitance should be within the range marked on the capacitor. Sometimes the range is marked as for example ±5% or it could be marked as a range. If the value on the meter isn’t within range or reads zero, the capacitor needs replacing.

Can You Test the Capacitor Without a Multimeter?

If you don’t have a multimeter or don’t want to buy one, how can you test a pool pump capacitor? There aren’t any other tests you can do but given that the cost of a capacitor is fairly cheap if you’re experiencing any of the signs listed above, go ahead and replace the capacitor.

Then you’ll know for sure if the capacitor is at fault.

Pool pump motor capacitor terminals.
Pool pump motor capacitor terminals | Credit: Chris Dill of Dill’s Repairs

How Much Does It Cost to Replace a Pool Pump Capacitor?

Pool pump capacitors aren’t expensive, so you won’t have to worry about putting a huge strain on your wallet to replace the capacitor.

While it varies depending on the manufacturer you choose, how many capacitors you need, and the recommended voltage, pool pump capacitors start as low as $9 each and cost around $25 at most.

Where to Buy Pool Pump Capacitors?

Do you need a pool pump capacitor fast? You can purchase them from plenty of retailers.

You can shop your favorite online retailers such as Amazon. Some home improvement stores carry capacitors but double-check that they’re pool pump capacitors before you buy them.

You can also stop into or visit the website of any of your preferred pool supply stores to stock up on capacitors to last you the whole season and beyond!

New pool pump motor start capacitor.
New pool pump motor start capacitor | Credit: Chris Dill of Dill’s Repairs

How to Replace a Pool Pump Capacitor

Are you a DIY type and you want to replace your pool pump capacitor yourself? Here are step-by-step instructions so you can get it done.

Step 1 – Power Down Your Pool

The pool pump, at the very least, should be powered off when replacing the capacitor(s). Turn off the pump at the breaker too and double-check there is no power running to the motor or the pump timer.

Step 2 – Access the Capacitor

You know where to find the pool pump capacitor by now, so this next step shouldn’t be a big deal. Be sure to remove the screws on the pump motor that keep the housing attached to the capacitor.

Step 3 – Discharge the Capacitor

As you did before, you need to short out the capacitor so it can discharge the electricity it’s built up. The same method as explained earlier is fine to repeat again.

Step 4 – Detach the Capacitor’s Motor Leads

With a multimeter, measure the voltage of the capacitor. If it is zero, free the capacitor by removing the motor leads attached to it. Don’t just throw them all willy-nilly, as you’ll need to remember how they were placed when you add the new capacitor shortly.

Step 5 – Reconnect the Motor Leads to the New Capacitor

Now that you’ve got your new pool pump capacitor all ready to go, reattach the motor leads, remembering how they were connected to the old capacitor when you detached them.

Step 6 – Put the Cover Back on the Capacitor

Whether you use the same plastic housing your old capacitor had or another one, don’t forget to sheath the new pool pump capacitor.

Step 7 – Reconnect Power and Test

Finally, you want to restore power to your swimming pool pump and see if the new capacitor is working. You’re finished!

Can I Use a Higher or Lower Capacitor Voltage?

You may have checked and can’t find a capacitor with the same voltage as the current capacitor. The good news is that it is safe to use a pool pump capacitor with a higher voltage than recommended. But do not use a capacitor with a lower voltage rating.

A lower voltage rating will result in the capacitor blowing.

Can I Use a Capacitor with Higher or Lower Capacitance?

In most cases, you want to get a capacitor with very similar values to the original. Pool pump capacitors are usually measured in microfarads (µF) or farads (F). You’re usually OK to install a capacitor that is within 10% of the previous one. But don’t make it substantially different. The motor will likely not run.

Related Reading: How to Fix Pool Pump Tripping Circuit Breaker (Repeatedly)

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