Troubleshooting
Why Your Well Jet Pump Keeps Losing Prime
A jet pump can only move water when it is full of water. If you have to re-prime it more than once, something is letting that water out or letting air in.
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A jet pump loses prime when the water in the pump and suction pipe drains away or is replaced by air. Pentair's troubleshooting chart names two causes for a pump that was working: air leaks on the suction side, and a water level that has fallen below the suction pipe inlet.[1] A leaking foot valve is the third usual suspect. Re-priming gets you water today; finding the leak is what stops it from happening again.
This guide is for jet pumps — the kind with a motor you can see, above ground. Submersible pumps sit under water and don't need priming; if yours runs without delivering water, see pump runs but no water.
Two warnings from the manufacturer
- Never run the pump dry. Pentair says running without water may overheat the pump, damage the seal and cause burns to anyone handling it.[1]
- Never run the pump against a closed discharge. Pentair warns this can boil the water inside the pump, creating hazardous pressure, a risk of explosion and scalding.[1]
Turn the breaker off before removing any plug, and let a hot pump cool for 20 minutes before touching it.
Why prime matters
A jet pump moves water by spinning it. It can't pump air, so if the pump body or the suction pipe holds air instead of water, the impeller spins without pulling anything up. A valve at the bottom of the suction pipe — the foot valve — is what keeps the pipe full when the pump stops.
Jet pumps pull (suction) or recirculate water through an ejector; submersibles push. Depth figures are manufacturer guidance for shallow-well jets (Pentair: a deep-well package may be needed beyond 25 ft to water).
How to re-prime (Pentair's procedure)
Follow your own pump's manual first. This is the sequence Pentair gives for its shallow-well jet pumps:[1]
- Power off. Switch the pump's breaker off and open a faucet to release any pressure.
- Fill the pump. Remove the priming plug and fill the pump with clean water. Fill all the piping between the pump and the well. If there is a priming tee on the suction pipe, fill it there too.
- Replace all fill plugs.
- Power on. If there is no water after 2 or 3 minutes, stop the pump, remove the plugs and refill. Pentair notes you may have to repeat this several times to get all the trapped air out, and that a pump lifting water 25 feet may take as long as 15 minutes to prime.
- Check a full cycle. Once the pump builds pressure and shuts off, open a faucet until it restarts and watch the gauge through one or two cycles.
If it loses prime again: the causes
| Cause | Clue | What the manual recommends |
|---|---|---|
| Air leak on the suction side | Air spitting at faucets; prime lost while the pump sits | Check all connections on the suction line and the shaft seal; joints can be checked with soapy water |
| Water level below the suction inlet | Happens in dry spells or after heavy use | Lower the suction line into the water and re-prime. If the receding water level is more than 25 feet down, a deep-well pump is needed |
| Leaking foot valve or check valve | Prime drains away while the pump sits; pressure gauge drifts down | Replace the foot valve or check valve |
| Foot valve or strainer plugged, or buried in sand or mud | Flow fell off before prime was lost | Clean it; raise it above the bottom of the water source |
| Frozen pipes | Cold snap; exposed pipe in a pit or well house | Thaw the pipes; bury them below the frost line; heat the pit or pump house |
Finding a suction leak
Safe to check
- Look along the suction pipe from the pump toward the well for cracked fittings, loose unions and old threaded joints.
- With the pump running, brush soapy water on each accessible suction joint. On a pipe under suction, a leak pulls the suds in.
- Look under the pump where the shaft enters: drips or mineral crust point to the shaft seal.
- Do the pressure-hold test to see whether pressure bleeds back toward the well.
Leaks in the buried part of the suction line, and a foot valve at the bottom of the well, can't be seen. If the accessible joints are tight and the prime still disappears, that's where a contractor will look next.
When the real problem is depth
A shallow-well jet pump works by suction, and suction has a hard limit. Pentair's manual says that if the water level recedes past 25 feet, a deep-well pump is needed, and that a deep-well jet package may be required when water is more than 25 feet down.[1] If your pump holds prime in spring and loses it every August, the water table is the likely cause, and no amount of re-priming will fix it. Compare the options in submersible vs. jet pumps.
What repairs cost
HomeGuide lists a foot valve replacement at $150–$400 and a check valve at $150–$200, parts and labor; a complete shallow-well jet pump replacement runs $400–$1,000 installed and a deep-well jet $500–$1,400.[2][3]
Sources
- Pentair. Pro Shallow Well Jet Pumps — Installation & Operation Manual (P15001, 2023). Accessed Sept. 28, 2026.
- HomeGuide. How Much Does Well Pump Repair Cost? (article dated Aug. 6, 2025). Accessed Oct. 8, 2026.
- HomeGuide. How Much Does a Well Pump Cost To Replace or Install? (article dated Aug. 7, 2025). Accessed Sept. 28, 2026.
We cite manufacturer documentation and public agencies first. Read how we choose and check sources.