Editor's Note: This is the first entry of a two-part series. The second part will appear online and in AQUA Magazine in May.
Your pool pump is overheating, and you want to know why it's happening and how to fix it. This two-part story is about what causes pool pumps to run too hot, what you can expect moving forward if you suspect your pump is overheating and some ways to remedy the problem.
Pool pumps use a lot of power, and as a result, they must dissipate large amounts of heat as part of normal operation. Combine that with the fact that most pool pumps operate in direct sunlight during the hottest part of the year, and you have the potential for an overheated motor. Most electric motors have a thermal disconnect designed to cut the power if the pump overheats, which should prevent the pump from catching on fire...usually. Clearly, it happens (as evidenced by the photo on this page) as there is more than enough power, and friction, in a pump to catch fire.
A pool pump can overheat in two ways: because of an electrical problem or friction. While electrically related failures are by far the most common cause for pump overheating, as we will discuss at length, there is also the potential for a friction fire to develop if a pump is starved for water. This is the case for the burnt pump casing that you see in the photo — this pump was operated with no water for an extended period of time.
The friction from the impeller spinning was enough to melt and ultimately ignite the pump. While uncommon, this is one of the reasons why proper care and maintenance for your pool is important. Even a closed valve that should be open can be enough to cause a pool pump to catch on fire — although this is a rare problem in comparison to electrical failures in pool pumps. By far, the largest cause of your pool pump being too hot is a degenerative process where heat and age cause the pump to draw too much current.
How Hot Is Too Hot?
All electric motors run hot and pool pumps are no different. But how hot is too hot for a pool pump? The first test is simply whether you can touch the motor or not.
Under normal operating conditions, the motor end of the pump is hot enough that you can barely touch it — but not searing hot. If you check your pool pump motor and find it is far too hot to be able to touch with your hand, that's not good. You should be able to place your hand on the motor for at least a few seconds without getting burned. If your pump is so hot that you cannot even rest your hand on top of the motor, it may be a sign that something internal on the pump is failing.
Once a heat-related failure is experienced, a downward spiral effect has started that will most likely result in the pump failing completely. The pump usually won't just turn off. Before a pump will turn itself off (thermally disconnect), the problem will need to be fairly severe. It is not uncommon for pumps with heat damage to run for a few days, up to a year or more, before they finally deteriorate to the point that you will need a new pump.
Why Is My Pool Pump So Hot?
A residential pool pump uses a standard electric motor, which is usually between 1/2 hp up to and including 3 hp. From electrical theory we know that 1 hp is equal to 746 watts of power. Right away it's obvious that this amount of power has the potential to generate a lot of heat. A 100-watt light bulb is far too hot to touch. A large 3-hp pool pump might generate almost 2,240 watts of power, which is more than sufficient to generate extremely large amounts of heat — and this does not even factor in the heat also being generated by friction from the moving parts inside of the pump.
Heat is a byproduct of energy loss. A pool pump is no different than other electric motors in that most of the energy fed into the pump is not converted into useful mechanical energy, but instead lost from the system in the form of heat. Even brand new out of the box this would be normal operation for a pool pump (or any typical electric motor).
However, the problem with most pool pumps that are too hot is that something has gone wrong, which is causing additional heat to be generated. While the pump is designed to dissipate heat through mechanical heat sinks and air-cooling, additional heat generated over and above what the pump is designed for can, and will most likely, cause a pump failure.
There are many reasons why your pump might be generating extra heat; these four are the most common:
Friction. There are multiple moving parts inside of a pool pump. Any moving part will generate heat from friction. Under normal conditions this amount of heat does not pose a problem for pool pumps as they will self regulate their heat. Ambient air is drawn through the motor to help keep it cool, and heavy pieces of metal (heat sinks) are designed to safely absorb heat that builds up.
One of the most common ways pool pumps will generate friction is from corroded bearings inside the pump. The shaft of the motor has bearings, which are designed to prevent wear and tear to moving parts. As these bearings dry out and begin to fail, a large amount of heat will be generated.
Bearings on pool pump motors usually fail when they start to rust. Once the bearings in the pump have begun to rust, it's just a matter of time before you have a pump failure. The telltale sign of rust on your pump bearings is a high-pitched squealing sound. This squealing sound is the sound of the bearings rubbing and generating friction at an extremely high speed.
Where oil once caused the bearings to move with next to no resistance, there is now a great deal of resistance, and heat, being generated. The main cause for this type of pump failure is a lack of simple maintenance. If the pool pump is leaking, whether from the main seal on the underside of the pump or from the pressure side connections, this must be resolved to prevent bearing failure.
Many pool owners do not notice, or simply ignore, small leaks in the equipment room, so it's on you as the service professional to discover these faults and take immediate action.
Lack Of Airflow. In order for most common electric motors to stay cool, air must be drawn into the motor and over the electric windings. This relatively cool air pulls heat from the motor before passing out the backside of the pump. This is why these types of pool pumps should only be installed in areas with sufficient airflow.
If you install a pool pump in a very small closet, or any kind of enclosed space, you will dramatically reduce the service life that you can expect from the pump. The motor will still draw in air but the air inside the closed space will soon be heated from this energy transfer. If the air inside the pump location is too warm, it will no longer be able to effectively cool the motor.
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This type of motor failure won't happen immediately, but will instead manifest into a situation each new pump only lasts a handful of years at most. A pool pump should last seven years at a minimum, hopefully much more, before needing service, repairs or replacement. If you are only getting a few years out of each motor, then there may not be enough airflow in the pump location for it to adequately cool itself.
If you are interested in protecting pool equipment as much as possible, the best situation would be to install a sunshade over the equipment pad. Closed-in rooms can work, but can also be a restriction for air unless an active ventilation system is added. A roof shelter over the equipment would be ideal to protect from direct sunlight while providing maximum airflow around the equipment.
Suction-Side Restrictions. Flow restrictions in the plumbing system should be minimized as much as possible. Coming into the suction side of the pump, there should be a straight, unobstructed run at least 10 times the pipe diameter in length. But as I've discovered, hardly any residential pool pumps are installed this way. Most installers give little thought to the flow dynamics of a pump when installing it. If you see a pool pump with a 90-degree fitting directly in front of the suction side, the pump will need to work harder than a pump with a straight, unobstructed run into it.
These friction losses in the pipe are made worse by turbulence. Slow-moving water flows smoothly and has the minimum amount of friction loss. As water moves faster, and becomes more turbulent, the efficiency of how the water moves through the pipe drops. That's true anywhere in your plumbing system, but nowhere is it more important than where the water enters your pump. You want the water to enter the suction side of the pump with as little turbulence as possible. Having a 90-degree fitting, street elbow, check valve, union or ball valve directly in front of the pump suction will dramatically increase the turbulence of the water, which will result in an efficiency loss for your pump.
Pressure-Side Restrictions. It's also critical to minimize resistance on the pressure side. Taking a large pump with a 2 or 3 hp motor and forcing the flow through a heavy-flow restriction — such as a filter that is too small, or plumbing that is too small — will cause the pump to work harder than it needs to. Picture yourself on a bike riding as fast as you can...if you are riding into a strong headwind, your performance and speed will drastically decline, and force you to use more energy to compensate.
This is similar to what your pump experiences when you have pressure-side flow restrictions. To avoid this problem, be sure to limit back-to-back plumbing fittings, which compound losses, and be sure that the pump is matched well with the other equipment and the demands of the pool.
This concludes Part 1, a discussion of the causes of overheating in pumps. Next month, in Part 2, we will talk about ways of preventing the problem and getting the longest pump life possible.
Comments or thoughts on this article? Please e-mail firstname.lastname@example.org.
Steve Goodale is a second-generation swimming pool expert located in Ontario, Canada. You can learn more about Steve, as well as swimming pool construction, maintenance and repair from his website: SwimmingPoolSteve.com.