A pump that spins without moving water is not broken. It is almost always empty, and five gallons of water fixes it.
Priming takes ten minutes. Knowing why the prime went missing in the first place is what stops you doing it again next week.
How Do You Prime a Well Pump?
Priming a well pump means filling the casing and suction line with water before starting it. Switch off the power, open the priming plug, fill until it overflows, replace the plug and start the pump, then watch the gauge for pressure within about a minute.
Key Takeaways
- Power off before the plug comes out, every time.
- Fill the suction line too, not just the casing.
- Use clean water, never gritty or pond water.
- Stop after 60 seconds if no pressure builds.
- Losing prime repeatedly means a suction-side leak.
The Procedure Step by Step
| Step | Action | Why it matters |
|---|---|---|
| 1 | Kill power at the breaker | The pump can start unattended |
| 2 | Open a downstream faucet | Lets trapped air escape |
| 3 | Remove the priming plug | Access to the casing |
| 4 | Fill until it overflows | Casing and pipe both full |
| 5 | Replace plug, restore power | Ready to start |
| 6 | Watch the gauge 60 seconds | No pressure means stop |
Step six is the one that saves pumps. Running a pump that has not caught prime is running it dry, and the damage starts immediately rather than after several minutes.
Why Running Dry Is So Costly
The mechanical seal depends on a film of water microns thick to lubricate and cool its faces. With no water there is no film, the faces overheat, and a seal that had years left starts weeping.
The details are in our pump mechanical seal guide. That is why an unsuccessful prime is worth stopping and diagnosing rather than attempting five times in a row.
When Prime Will Not Hold
- Failed foot valve letting the suction line drain back.
- Leaking suction joint drawing air rather than leaking water.
- Cracked suction pipe above the water line.
- Water level dropped below the suction intake.
- Worn impeller unable to build enough suction.
Suction leaks are counterintuitive because they show no drip. The pipe is under vacuum while the pump runs, so it pulls air in rather than pushing water out. The foot valve is the more common of the two, and it is covered in our foot valve guide.
Pumps That Prime Themselves
Self-priming pumps keep a reservoir of water in the casing so they can clear air from the suction line without help. They still need that first fill, and they still cannot run dry, but they recover on their own after that.
The differences are set out in our comparison of centrifugal and self-priming pumps. Submersibles sidestep the question entirely by sitting below the water, and general well construction is described by the USGS. Jet pumps are the ones that demand the most care, as covered in our shallow well jet pump guide.
Frequently Asked Questions
How much water does it take to prime a well pump?
Priming a well pump usually takes five gallons or more, because you are filling the whole suction line as well as the pump casing, and the pipe holds far more than the casing does. Keep pouring until the priming port overflows rather than measuring it. Use clean water, never gritty or pond water.
What is the best way to prime a well pump?
The best way to prime a well pump is to kill the power, open a downstream faucet to let air escape, remove the priming plug and fill until it overflows. Replace the plug, restore power and watch the gauge. If no pressure builds within about a minute, stop rather than repeating.
What happens if you don’t prime a well pump?
If you don’t prime a well pump it spins without moving water, because a centrifugal impeller cannot grip air. Worse, the mechanical seal loses the film of water that lubricates and cools its faces, so they overheat within seconds. A few dry starts will finish a seal that had years left.
What do I do if my well pump loses prime?
If a well pump loses prime repeatedly, stop re-priming it and find the air leak instead. The usual culprit is a failed foot valve letting the suction line drain back down the well, followed by a leaking suction joint or a cracked pipe. Suction leaks draw air in and show no drip.
How do you get pressure back in a well pump?
Getting pressure back in a well pump starts with priming it properly, then checking the pressure tank’s air charge and the switch settings, because a switch set to 20/40 simply cannot deliver more than that. If the tank and the switch are both right and pressure still will not build, the impeller is the next suspect.
Well Pump Help at Ken’s Distributing
Ken’s Distributing supplies foot valves, suction fittings and pumps across the Franklin Electric range and the Monarch water pump range.
If a pump will not hold prime for more than a day, send us the setup details and we will work out which part of the suction side is letting air in before you replace the pump.