If your faucets are sputtering or there's no water at all, you probably need to know how to prime a jet pump before you call an expensive plumber. It's one of those basic homeowner skills that sounds a lot more intimidating than it actually is. Most people panic when the water stops, thinking the pump has died or the well has run dry, but usually, it's just a bit of trapped air causing the system to lose its "prime."
In simple terms, a jet pump isn't like a vacuum cleaner that can just suck up air and eventually get to the water. It needs water to move water. If air gets into the line, the impeller just spins fruitlessly, like a car tire spinning in deep mud. To get things moving again, you have to manually fill the pump and the suction line with water.
Why do pumps lose their prime anyway?
Before we get into the "how," it's worth asking "why." If this is the first time it's happened after a power outage or because you were doing some plumbing repairs, don't worry—it's normal. However, if you find yourself doing this every week, you've likely got a bigger issue.
Common culprits include a leaky foot valve (the one-way valve at the bottom of your well), a tiny hole in the suction pipe, or even a drop in the water table. But for today, let's just focus on getting your water pressure back so you can finally take a shower or run the dishwasher.
Getting your tools ready
You don't need a massive toolbox for this. Usually, a pipe wrench or a large pair of adjustable pliers will do the trick. You'll also need a source of clean water—a couple of five-gallon buckets or a few gallon jugs should be plenty.
If your pump is completely dry, you might need more water than you think, especially if the suction line is long. Oh, and grab some thread seal tape (Teflon tape) if you have it. It's always a good idea to re-wrap the prime plug before you put it back in to ensure an airtight seal.
Step 1: Safety first
I know it sounds like a cliché, but seriously, turn off the power. Find the circuit breaker for the pump and flip it to "off." You're going to be working with water around electrical components, and the last thing you want is the pump suddenly kicking on while your hands are near the motor or while you're pouring water into the housing.
Step 2: Locate the priming plug
Look at the top of the pump housing (the heavy metal part, not the motor). You should see a small square or hex-headed plug. This is the priming port. Sometimes it's located on a tee-fitting right above the pump.
Using your wrench, slowly unscrew this plug. Don't be surprised if there's a little bit of "hissing" or a small splash of water—that's just the pressure releasing. Set the plug aside somewhere safe where it won't roll away into a dark corner of the basement or crawlspace.
Step 3: Fill the pump with water
This is where the actual priming happens. Stick a funnel into the hole and start pouring your clean water in. You want to fill the pump housing until the water stays at the very top of the hole and doesn't disappear down the pipe.
If you pour water in and it immediately vanishes, that means it's running down the suction pipe toward the well. This is actually a good thing! It means you're filling the whole line. Keep pouring until it stabilizes and stays level with the opening. If it never fills up, you might have a bad foot valve at the bottom of the well that's letting all the water leak out as fast as you can pour it in.
Step 4: Seal it back up
Once the water is sitting steady at the top of the port, it's time to put the plug back. This is where that Teflon tape comes in handy. Wrap a couple of layers around the threads of the plug to make sure no air can leak in.
Screw the plug back in by hand first to make sure you don't cross-thread it, then tighten it down with your wrench. It needs to be snug, but don't go overboard and crack the housing. We're looking for "firmly tight," not "Herculean effort tight."
Step 5: The moment of truth
Go ahead and flip the breaker back on. You'll hear the motor start to hum. Now, don't expect instant, perfect pressure. The pump might sound a bit "chattery" or loud at first as it works through the remaining bits of air.
A pro tip: keep a faucet somewhere in the house open (preferably one without an aerator, like a laundry tub) while you do this. This gives the air a place to escape. If the pump runs for a minute or two and the pressure gauge starts to climb, you've nailed it. If the pressure doesn't move and the pump just keeps humming without getting anywhere, you'll need to shut it off and repeat the process.
Sometimes once isn't enough
Don't get discouraged if it doesn't work on the first try. Depending on how much air was in the line, you might have to prime it two or three times. It's annoying, but it's just part of the process. Each time you prime it, you're essentially "chasing" the air out.
If you've tried four or five times and the pump still isn't catching, you might have a "suction leak." Even a pinhole-sized leak in the pipe leading from the well to the pump will prevent it from ever building pressure. Think of it like trying to drink through a straw that has a crack in it—no matter how hard you suck, you're mostly just getting air.
Troubleshooting common priming issues
If you're struggling with how to prime a jet pump and the standard steps aren't working, here are a few things to check:
- The Foot Valve: As I mentioned earlier, this valve is supposed to keep water in the pipe when the pump shuts off. If it's stuck open or clogged with debris, your prime will drain away every time the pump stops.
- The Pressure Switch: Sometimes the pump is primed fine, but the pressure switch is gunked up and isn't telling the pump to turn on or off at the right times.
- Deep Well vs. Shallow Well: If you have a deep well jet pump (one with two pipes going into the well), the process is the same, but it can take a lot more water to fill those lines. Be patient.
- Frozen Pipes: If it's the middle of winter, check for ice. A frozen suction line will make priming impossible.
Keeping your pump happy
Once you've got the water flowing again, you probably want to make sure you don't have to do this again anytime soon. The best thing you can do is keep an eye on your pressure gauge. If you notice the pressure dropping slowly when no water is being used, you likely have a small leak somewhere that will eventually cause the pump to lose its prime again.
Also, if your pump is located in a damp basement or an outdoor well house, make sure it stays relatively clean and dry. Corrosion on the priming plug can make it a nightmare to remove the next time you need to get in there. A little dab of waterproof grease on the threads can save you a lot of swearing in the future.
When to call in the pros
Look, I'm all for DIY, but sometimes a pump is just toast. If you hear the motor making a high-pitched screaming sound, or if it's getting extremely hot to the touch while you're trying to prime it, the bearings or the impeller might be gone. At that point, no amount of pouring water into the priming port is going to help.
But for 90% of water pressure issues, knowing how to prime a jet pump is the only "magic trick" you need. It's a bit messy, and it requires some patience, but the satisfaction of hearing that pump finally click off because it reached full pressure is worth the effort. Now go take that shower—you've earned it!