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Priming an irrigation pump means filling the pump housing and suction line with water before the pump starts. This removes most of the air so the pump can pull water from a pond, tank, cistern, rainwater storage system, or shallow well.
Most above-ground centrifugal irrigation pumps need to be primed before their first use and any time the suction side loses water. Do not let the pump run dry. Running without water can damage seals and other pump parts.
Before You Prime the Pump
First, make sure the pump actually needs manual priming.
A typical above-ground irrigation pump may need priming if:
- It is being started for the first time.
- The suction pipe was drained or disconnected.
- The pump has been sitting unused.
- A check valve or foot valve leaked and let the water drain back.
- The pump runs but does not move water.
Some pumps are sold as self-priming. They still usually need water in the pump housing before the first startup. "Self-priming" does not normally mean the pump can start completely dry.
Submersible pumps are different. They operate underwater and are not normally primed this way.
Check the pump manual before opening plugs or starting the motor.
What You Need
For most irrigation pumps, you only need:
- Clean water
- A funnel or small container if the fill opening is hard to reach
- The correct wrench or hand tool for the priming plug, if required
You should also check the suction pipe, fittings, valves, and water source before starting.
How to Prime an Irrigation Pump
1. Turn Off Electrical Power
Switch off the pump and disconnect power before removing the priming plug or working around the pump.
Water and electricity are a dangerous mix. Do not work on wiring, switches, or electrical connections unless you are qualified to do so.
2. Check the Water Source
Make sure there is enough water for the suction inlet to stay submerged while the pump runs.
For a rainwater cistern or tank, confirm that the water level is above the intake. For a pond or shallow well, make sure the intake has not become exposed.
A pump cannot stay primed if it keeps pulling air into the suction line.
3. Check the Suction Side
Look over the pipe or hose running from the water source to the pump.
Check for:
- Loose threaded fittings
- Cracked pipe or hose
- Missing seals or gaskets
- An open drain valve
- A leaking check valve
- A damaged foot valve
The suction side must be very close to airtight. A connection can sometimes pull air inward without leaking much water outward.
A foot valve is a one-way valve installed near the bottom of a suction pipe. It helps keep water from draining back into the source when the pump stops.
A check valve serves a similar purpose by allowing water to move in only one direction.
4. Open the Priming Port
Find the priming or fill plug on the pump housing.
Slowly remove it while the pump is off.
Do not confuse the priming plug with a drain plug. The pump manual should show the correct opening.
5. Fill the Pump With Water
Pour clean water into the priming opening.
Fill slowly so trapped air has time to escape.
On many systems, you continue adding water until the pump housing is full and the water level stays near the top of the opening.
If the suction pipe is empty, it may take more water because you are filling part of that line as well.
Do not pour water over the motor or electrical parts.
6. Replace the Priming Plug
Reinstall the plug once the pump is full.
Tighten it enough to seal properly, but do not overtighten a plastic plug or housing.
An air leak around the priming plug can keep the pump from developing suction.
7. Set the Discharge Valve as Required
Follow the pump manufacturer's startup instructions for the discharge valve.
Some systems should start with the discharge partly open. Others have different requirements.
Avoid closing valves in a way that could create unsafe pressure in the pump or irrigation plumbing.
8. Restore Power and Start the Pump
Turn the pump on.
Water should begin moving after the pump clears the remaining air from the suction line.
The exact time depends on the pump, suction pipe length, vertical lift, and system design.
Do not leave a pump running for an extended period if it is not moving water. Shut it off and investigate the problem rather than hoping it will eventually prime.
9. Check the Flow
Once water starts moving, look for steady flow from the irrigation system.
Watch for:
- Surging water
- Large amounts of air
- Unusual pump noise
- Loss of pressure
- Water leaking from fittings
- The pump repeatedly losing prime
A steady flow usually means most of the air has cleared.
Why an Irrigation Pump May Not Prime
If you fill the pump but it still will not move water, simply adding more water may not solve the problem.
There Is an Air Leak
Guidance on manually priming a water pump helps assess signs that pressure trouble begins on the suction side.
Air leaks on the suction side are one of the most common causes of priming trouble.
Check threaded fittings, unions, hose connections, valve stems, gaskets, and the priming plug.
Even a small leak can stop a centrifugal pump from creating enough suction.
The Foot Valve Is Leaking
If the pump primes successfully but loses prime after sitting, the foot valve or check valve may not be holding water.
Debris can also keep a valve from closing completely.
The Suction Intake Is Above the Water
The intake must remain submerged.
Rainwater tanks can create this problem when the stored water level falls below the outlet or floating intake.
The Pump Is Too High Above the Water
A pump can only lift water so far on its suction side.
This vertical distance is often called suction lift. The greater the lift, the harder it is for the pump to draw water.
Manufacturer limits matter because real installations lose some performance through pipe friction, fittings, elevation, temperature, and air leaks.
If the water source is far below the pump, priming problems may be a sign that the pump or system layout is not suitable.
The Suction Pipe Is Restricted
A clogged screen, blocked foot valve, collapsed hose, dirty intake, or undersized pipe can reduce flow into the pump.
Long suction lines and too many restrictive fittings can also make priming harder.
The Pump Is Spinning but Not Pumping
Possible causes include a blocked impeller, damaged internal parts, a failed seal, incorrect installation, or a pump that is not suitable for the required lift and flow.
Stop troubleshooting if inspection would require opening electrical equipment or dismantling a pump beyond normal owner maintenance.
How to Keep an Irrigation Pump Primed
A properly installed system should not normally need to be manually primed before every irrigation cycle.
If yours does, look for the reason it is losing water.
Good practices include:
- Keep the suction system airtight.
- Use a suitable check valve or foot valve where the system requires one.
- Keep the intake submerged.
- Clean intake screens when needed.
- Repair leaking fittings.
- Protect suction piping from physical damage.
- Follow the pump manufacturer's maintenance schedule.
Repeated loss of prime is usually a system problem, not a normal operating step.
Priming a Pump From a Rainwater Tank or Cistern
The same basic priming process applies when an irrigation pump draws from stored rainwater.
The main difference is the tank connection.
Check that:
- The tank contains enough water.
- The outlet valve is open.
- The intake is not blocked by sediment.
- The suction connection is sealed.
- Any check valve is installed in the correct direction.
- The pump is within its allowed suction-lift range.
A flooded suction arrangement can make operation easier. This means the water level in the tank is above the pump inlet, so gravity helps keep water at the pump.
When possible, this is generally easier to prime than a system where the pump must lift water from below.
Collected rainwater can contain grit, leaves, insects, roof debris, and sediment. A suitable intake screen or prefilter can help protect irrigation equipment, but it should not restrict the pump more than the system allows.
Do You Need to Prime After Winter?
You may need to prime an irrigation pump after winter if the pump and suction line were drained for freeze protection.
Inspect the system before restarting it.
Look for split pipes, loose fittings, damaged valves, cracked housings, and failed seals. Freezing water can damage components even when the damage is not immediately obvious.
Do not run a pump with a cracked housing or damaged electrical equipment.
When to Stop and Get Help
Basic priming and visual checks are reasonable DIY tasks for many irrigation systems.
Get qualified help if:
- The pump trips breakers repeatedly.
- Wiring or electrical controls appear damaged.
- Water has entered electrical components.
- The pump housing is cracked.
- The pump repeatedly runs dry.
- The pressure system behaves unpredictably.
- You cannot find the cause of repeated prime loss.
- The installation requires changes to mains-voltage wiring or pressure controls.
A pump that continually loses prime usually needs a leak, valve, intake, or installation problem corrected rather than repeated manual filling.
Frequently Asked Questions
How do I know when an irrigation pump is fully primed?
The pump housing should be full of water before startup. After the pump starts, a steady discharge with little or no air usually shows that the suction line has filled and the pump is moving water normally.
Can I prime an irrigation pump while it is running?
Normally, no. Turn the pump off before removing the priming plug and adding water. Opening a pump housing while equipment is running can expose you to moving parts, water pressure, and electrical hazards.
How many times should I try priming a pump?
If one or two careful priming attempts do not work, stop and look for an air leak, leaking check valve, blocked intake, excessive suction lift, or another system problem. Repeatedly running the pump without water can cause damage.
Why does my irrigation pump lose prime overnight?
Water may be draining back through a leaking foot valve or check valve. An air leak in the suction piping can also let the line lose water while the pump is off.
Can I use a garden hose to prime an irrigation pump?
A hose can sometimes be used to supply clean priming water if you can do so without spraying the motor or electrical equipment. Follow the pump manufacturer's filling instructions and do not pressurize openings that are not designed for it.
Does a self-priming irrigation pump need water added?
Usually, yes, before its first startup or after the pump housing has been drained. Self-priming pumps are designed to clear some air from the suction line after their casing contains the required amount of water.
Why does my pump sound like it is running but no water comes out?
The pump may not be primed, the intake may be exposed or blocked, the suction line may be leaking air, or the pump may be trying to lift water farther than it can handle. Shut it down rather than letting it continue to run dry.
