A jet pump that loses prime won't build pressure no matter how long it runs. Here is exactly how to reprime it — and what caused it to lose prime in the first place.
Priming a well pump means filling the pump and suction pipe with water so the pump can create suction and draw water up from the well. Jet pumps (above-ground pumps) rely on water to create the partial vacuum needed to lift water. When air gets into the system, the pump can no longer create that vacuum and stops producing water.
Note: Submersible pumps are always submerged in water and do not need to be primed. This guide is for jet pumps only.
Flip the pump breaker to OFF before doing anything. Never work on a pump while it is energized. Running a pump dry (without water) even for a few minutes can permanently damage the pump seal.
Find the priming plug on top of the pump housing — it is usually a large bolt or plug, often 1/2 inch or 3/4 inch. Place a bucket underneath before removing it, as trapped water will drain out.
Using a garden hose, pitcher, or bucket, slowly pour water into the priming plug opening. Keep pouring until water flows back out of the hole — this means the pump housing and suction pipe are completely full with no air pockets remaining.
Reinstall the priming plug and tighten firmly. Use Teflon tape on the threads if there is any sign of leakage. Do not over-tighten — snug plus a quarter turn is sufficient on most pump housings.
Turn the breaker back ON. The pump should start immediately and begin building pressure. Watch the pressure gauge — it should rise to cut-out pressure within 60-90 seconds. If it builds pressure normally, priming is complete.
If pressure does not build after 2-3 minutes, turn the pump off immediately to prevent damage. The suction pipe may have a leak, the foot valve at the bottom of the well pipe may be stuck open, or the well water level may be too low for the pump to draw from. At this point, a well contractor should inspect the system.
Common causes include: a leaking suction pipe joint allowing air into the line, a failed foot valve (check valve at the bottom of the suction pipe) that lets water drain back into the well, running the pump dry, or servicing the system and not refilling before startup.
A properly functioning jet pump system should rarely if ever need repriming. If you find yourself priming the pump every few weeks or months, that points to an underlying problem such as a failing foot valve or a leaking suction line joint, not something to just keep working around.
No. Submersible pumps sit below the water line inside the well casing and are always surrounded by water, so they cannot lose prime the way above-ground jet pumps can. If a submersible pump is not producing water, the cause is something else entirely, such as a failed pump, a tripped breaker, or a low water table.
Most residential jet pumps need anywhere from a quart to a gallon or more to fill the pump housing and suction line completely. Keep pouring until water flows steadily back out of the priming plug opening with no air bubbles, rather than stopping after a fixed amount.
This usually points to a suction pipe joint below or near the water table that is drawing in air intermittently, often worsened by ground movement or saturation after rain. A pressurized leak test on the suction line will usually find the joint, and it should be resealed or replaced rather than reprimed repeatedly.
Yes. A brand new jet pump installation is dry until you fill it for the first time, so priming on initial startup is expected and not a sign of a problem. After that first prime, a properly sealed system should hold prime indefinitely.
An undersized tank causes low pressure and short cycling. Check yours free in 2 minutes.
Use the Free Calculator →