How To Replace a Hot Tub Pump Shaft Seal

The hot tub pump may often seem like a tricky and dangerous little bit of machinery. We know that it needs to work properly, but we may not often know everything we should do to help it run the right way.

One of the basic things we can do as hot tub owners is to maintain the hot tub pump shaft seal and replace it if necessary. Although it may seem like a daunting task, it’s really not that difficult with a little helpful research.

The Leak

A hot tub pump shaft seal can wear out over time, requiring it to be replaced. You’ll probably start to notice some hot tub water leaking from your pump and upon closer inspection, should be able to tell where that leak is originating.

To do this, open your spa cabinet where your pump is and use a flashlight to examine your hot tub pump. If you have a pump with an open volute (meaning you can see the motor shaft), a leaking shaft seal will leak where the shaft enters the volute, creating a thin, running stream of water.

If your pump has a closed volute (meaning you CAN’T see the motor shaft), the water will be leaking out of a drain hole in the bottom of the seal plate or the point where the motor joins the wet end of the spa pump.

Replacement Seal

Once you’ve established that your hot tub leak is due to the pump shaft seal, you’ll need to order a new one. To order the correct seal, order based on the make and model of the pump itself. If it isn’t clearly written on the side of the unit, check your owner’s manual. If THAT doesn’t work, you’ll need to disassemble the pump and measure it.

First, shut off the main breaker so no power is getting to the unit. Close the valves on both sides of the pump to keep the water from leaking—otherwise, you’ll need to do this part when the spa has been drained for a cleaning.

The rest of the instructions from Hot Tub Works are very helpful:

"Unscrew the unions on the pipes that come in and out of the pump (there will be some water spillage). Disconnect the bare copper bonding wire from the bonding lug. Remove the power cord from the control box. With the motor removed, and in a location that you can work on it (without stooping or laying on your stomach), loosen the bolts that secure the front plate to the volute.

With the front plate removed, you should be looking at the impeller. Some spa pumps have an impeller shroud, or diverter that will need to be removed first. Remove the impeller by holding the shaft firmly in place, while spinning the impeller in a counter-clockwise direction. For open volutes, a small pair of vice grips can be used to hold the shaft firmly so it won’t turn as the impeller is threaded off of the shaft.

For closed volutes, the trick is to hold the shaft in one location at the rear of the motor. For motors with a removal end cover, a 7/16 wrench can be used on the rear of the shaft. Others have a small shaft cap that can be removed, dead center of the rear end bell of the motor. The shaft is slotted to accept a large flat head screwdriver, used to hold the shaft stationary.

After removing the impeller, you should see your shaft seal, and you can now identify it by type and size."

Choose the Right Seal

When you go to order your seal, it’s important that you pick the correct one, otherwise you’ll wind up with something ineffective that will degrade rapidly and lead to more leaking. In the past, hot tub pump shaft seals have been made of what are called Buna elastomers, a phenolic (plastic) carbon and ceramic mating ring. These materials are great for a seal that deals with small amounts of chlorine that are diluted before it interacts with the pump seal.

However, many modern hot tubs use alternative sanitizers like ozonators, salt chlorine, or hydrogen peroxide-based chemicals. Your typical seal system made of Buna elastomers will be destroyed quickly with these systems. If you have one of these seals installed with an incompatible system, the seals will discolor and the edges will deteriorate.

US Seal—which is a manufacturer of pump shaft seals—has made newer seals that react better with ozone, salt generators, etc. These are marked with an “Ozone/Salt” specification to let you know it’s compatible. These are constructed using Viton elastomers along with a resin-filled carbon ring and a superior-grade of ceramic. This means it’s manufactured to withstand the chemical output of ozone and salt, allowing for a longer life for your seal and fewer pump/motor issues.

Check the Pump

If you follow the steps above and you’ve disassembled your pump (the above YouTube video is a quick and dirty guide), now is a good time to check for any other damage. Get a work area that is clean and already prepared and get to work. Here are the things you should take a look at to make sure they’re working correctly:

• Inspect the overall condition of the pump and motor—note anything that seems to not be functioning properly and take care of that first. Fixing a broken seal when you have other major pump or motor issues is like putting a Band-Aid on a broken bone.
• Make sure the tracking on your primary ring (typically the black ring of the existing seal) is not irregular as this is a sign of a damaged impeller. This could also be because the back plate is not concentric with the centerline shaft. These two issues often lead to seal failure so it’s better to fix them while you have the opportunity.
• Check out the back plate—note whether or not the bore is clean and in good shape.
• Examine the shaft and be sure it’s not bent as this well add strain to your seals and other pump components.
• Look at the impeller or seal housing. If they are worn out, they should not be in continued use.
• Inspect the bearings to be sure they’re not loose, noisy, or need replacing.
• If you’ve ordered your seal, now is a good time to check it for cracks or damage from shipping, being careful not to touch the seal itself.

Clean the Parts

Before you install the new seal, take off the old one (noting how it was installed—the number one mistake people make is putting on the pieces incorrectly like putting in the mating seal upside down) and clean all the parts in preparation. Your equipment, work area, and the seal itself should stay clean. Ideally, you should wear latex gloves when installing a seal to make sure the oils from your fingers don’t affect how it adheres.

Installation

It’s recommended that you use some seal-specific lubricant for the installation. Use the wrong kind, and you will destroy the seal. Use a water based lubricant like US Seal Lube, NEVER a PTFE or silicon based lubricant that will draw carbon from the primary ring and cause a buildup that will degrade the seal itself.

Apply lube to the rubber parts of the seal only. DON’T apply the lubricant to the face of the mating ring. Be sure not to touch the seal itself, just the outer rings.

Don’t use an adhesive in place of a lubricant. This will cause fast seal failure.

Clean both sealing surfaces before reassembling the pump using something like rubbing alcohol and a clean cloth. These cleanings can add life to your hot tub pump as well as the seals.

Re-assemble the pump, turning the shaft by hand a few rotations and reconnecting the pump and motor to the rest of your hot tub system. Then flood the strainer with water and start the pump. NEVER RUN YOUR HOT TUB PUMP DRY. This will damage or destroy the seal.

Making Your Seals Last

To extend the life of your hot tub shaft seal, there are a few preventative measures you can take:

• Buy the correct variety for your sanitizer system (as noted previously)
• Never run the pump dry
• Maintain your water level, not letting it get too low or sit empty with parts still running—this will suck air into the system
• Maintain proper water chemistry

I know that seems like a lot of steps, but a hot tub pump shaft seal replacement is as complicated of an operation as you may think. If you’re comfortable making the repair, more power to you! It’s important to know your hot tub’s operating system inside and out.