Leaking Pump Shaft Seal: Signs and Replacement

The shaft seal is a small, inexpensive part that keeps water inside the pump where the motor shaft passes through. When it wears out, water drips out between the pump and the motor, and if you ignore it, that water can ruin the motor's bearings. This guide explains how to spot a leaking seal, how to choose the right replacement, and what the replacement job involves.

How a pump shaft seal works

A pool pump shaft seal is a two-part mechanical seal. One half, usually a ceramic ring in a rubber boot, sits still in the seal plate. The other half, a carbon face with a spring, turns with the impeller. The spring presses the two polished faces together, and a thin film of water between them keeps them cool and sealed. Running the pump dry overheats those faces, which is one of the most common reasons seals fail early. Age, chemical imbalance, and grit also wear them out.

Signs your shaft seal is leaking

• Water dripping or running from the gap between the pump housing and the motor, especially while the pump runs
• A puddle under the pump that keeps coming back
• Rust or mineral streaks on the motor's front end or shaft
• Squealing or grinding from the motor, which can mean water has already reached the bearings

Not every leak near the pump is the shaft seal. Check first for leaks at the pump lid, drain plugs, unions, threaded fittings, and the seal plate gasket or housing O-ring. If water comes from exactly where the motor shaft enters the seal plate, the shaft seal is the likely cause.

Choosing the right replacement seal

Seals come in many sizes and designs, and the right one depends on your pump model:

• Find the pump model on the pump label, then use the manufacturer's parts diagram or a seal cross-reference to get the seal part number.
• Compatible seals from specialist makers, such as U.S. Seal, Aquatic Pool Company, and Aladdin, often list the pumps they fit.
• If the pool uses salt or has warm water, some seal designs use materials meant to stand up to these conditions. Check the product description.
• Consider a seal and O-ring kit (often called a "go-kit") for your pump. It includes the shaft seal along with the housing, lid, and drain plug O-rings, so you can replace all of them while the pump is apart.

Shop seals, seal plates, and kits in Pump Seals & Seal Plates, and individual O-rings in O-Rings & Gaskets.

What the replacement involves

Safety note: Turn off power at the breaker before starting, and confirm the motor can't be started by a timer, controller, or automation system. If you need to disconnect the motor wiring, or you're not comfortable working on the pump, have a qualified pool technician or electrician do the job. Capacitors can hold a charge after power is off.

Steps vary by pump, so follow your pump's manual. The general process is:

1. Isolate and drain the pump. Close valves if you have them and remove the drain plugs.
2. Separate the motor from the pump housing. On most pumps, you remove the bolts or clamp holding the housing to the seal plate and slide the motor assembly out. The housing can usually stay plumbed in place.
3. Remove the diffuser and impeller. The impeller usually threads onto the motor shaft. Hold the shaft steady at the back of the motor while unscrewing it. Some impellers have a retaining screw with reverse threads; check your manual.
4. Remove the old seal. Take the spring half off the impeller and press the ceramic half out of the seal plate. Clean the seal plate bore and the impeller hub.
5. Install the ceramic half. Press it squarely into the seal plate, with the polished face pointing toward the impeller. Use only water or a light soap solution to ease it in if your seal's instructions allow, and don't use oil or grease on the seal faces.
6. Install the spring half onto the impeller hub, with the carbon face toward the ceramic face.
7. Keep the faces clean. Don't touch the polished seal faces with your fingers. Skin oils and grit can cause leaks. Wipe them only with a clean, soft cloth if needed.
8. Reassemble. Thread the impeller back on, refit the diffuser, replace the housing O-ring or gasket, and bolt the motor back to the housing evenly.
9. Prime before running. Fill the strainer pot with water before starting the pump, and never let a new seal run dry, even briefly.

A new seal may weep slightly for a short time as the faces bed in. A steady drip after that usually means the seal wasn't seated squarely, a face was damaged, or there's a different leak.

Check the motor while you're in there

If the motor was noisy before you started, or the shaft feels rough when you turn it, the bearings may already be damaged by water. Replacing the seal won't fix noisy bearings. In that case, consider a replacement motor from Pump Motors, and install a new seal with it. Also look at the impeller and diffuser for wear or cracks while the pump is open; see Pump Impellers & Diffusers.

Help your new seal last

• Never run the pump without water. Keep the water level up and the baskets clean.
• Keep the water balanced. Very low pH or high chlorine shortens seal life.
• Fix suction-side air leaks so the pump doesn't run partly dry.
• Replace the shaft seal whenever you replace the motor.

Not sure which seal fits your pump? Use the chat on this page or reach us through our contact page with your pump model, and we'll help you find the right seal or kit.