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An airlock in a water pump happens when trapped air stops water from moving through the pump or pipe. The pump may run but deliver little or no water. It may also lose its prime, make unusual sounds, or cycle without building normal pressure.
The usual fix is to shut the pump off, make sure the water source is available, release trapped air, refill or prime the pump if needed, and restart it with a clear path for water to flow.
Do not keep running a pump that is not moving water. Many pumps rely on water for cooling and lubrication, and running dry can damage them.
First, Make Sure It Is Really an Airlock
Several pump problems can look like an airlock.
Common signs include:
- The pump runs but little or no water comes out.
- Water comes out in spurts with bursts of air.
- The pump was recently drained, serviced, or installed.
- A rainwater tank or cistern recently ran low.
- The suction pipe was disconnected or emptied.
- The pump works after priming but loses flow again.
- You hear air moving through the plumbing.
An airlock is more likely after the system has been emptied or after air has entered the suction line.
If the pump keeps losing water after you remove the air, the real problem may be a suction leak, bad check valve, blocked inlet, low tank level, or another pump fault.
What Does Priming a Pump Mean?
Priming means filling the pump body and, on many systems, part of the suction pipe with water before starting the pump.
Many surface pumps cannot pull water properly when their pump chamber is full of air. The impeller may spin, but it cannot create normal suction until water reaches it.
Submersible pumps are different because the pump itself sits underwater. They normally do not need manual priming, although air can still become trapped elsewhere in the plumbing.
How to Remove an Airlock From a Water Pump
The exact procedure depends on the pump and plumbing layout, but the following approach works for many rainwater, cistern, and garden pump systems.
1. Turn Off the Pump
Switch off electrical power before opening fittings, removing a priming plug, or checking the pump.
If the system uses a pressure tank, there may still be pressurized water in the plumbing after the pump is switched off.
Open a faucet or outlet slowly to relieve pressure before loosening anything.
Never remove a plug or fitting from a pressurized pump.
2. Check the Water Level
Make sure there is enough water in the rain tank, cistern, barrel, or other supply.
The pump inlet must stay below the water level if the system depends on a submerged pickup.
Also check that:
- The inlet is not blocked by leaves or sediment.
- A tank valve has not been closed.
- A floating intake has not become stuck above the water.
- The suction hose has not collapsed.
- The pump has not been trying to draw from an empty tank.
Removing an airlock will not help if no water can reach the pump.
3. Open an Outlet or Vent Point
Air needs somewhere to escape.
Open a faucet, hose bib, irrigation valve, or other outlet downstream from the pump.
If the plumbing has a proper air vent at a high point, make sure it is working as intended.
Opening an outlet also prevents the pump from immediately pushing against a completely closed system when restarted.
4. Prime the Pump if Required
If you have a surface pump with a priming port, remove the priming plug only after power is off and pressure has been released.
Fill the pump casing with clean water until it stays full.
Depending on the design, you may need to wait while water settles into the suction line and then add more.
Replace the priming plug securely before starting the pump.
Do not pour water into electrical openings or parts of the pump that are not meant to be opened.
Follow the pump manufacturer's priming instructions when available because procedures vary between models.
5. Let Trapped Air Escape
Air often collects at high points in the plumbing.
With the pump properly primed and an outlet open, restart the pump.
Water may initially sputter from the open outlet. That is normal while trapped air is pushed out.
Let the water run until the flow becomes steady.
Then close the outlet gradually.
Do not let the pump run for an extended period if it cannot establish water flow.
6. Watch the Pump After Restarting
A successful fix should give you:
- Steady water flow
- Normal pump sound
- Normal pressure buildup
- Little or no air at faucets
- Normal pump cycling
If the pump immediately loses prime again, shut it off and look for the reason air is getting back into the system.
How to Remove Air From a Gravity-Fed Pump
A pump connected near the bottom of a rainwater tank may receive water by gravity.
This setup is often easier to bleed because water naturally moves toward the pump.
With the pump switched off and the tank outlet open, carefully open a suitable bleed or priming point if the system has one.
Water should eventually reach that point without bubbles.
Once the pump chamber and supply line are full of water, close the bleed point and restart the pump with an outlet open.
If water does not reach the pump by gravity, check for:
- A closed valve
- A blocked tank outlet
- A kinked pipe
- An uphill section trapping air
- A clogged strainer
How to Clear Air From a Suction-Lift Pump
A suction-lift system places the pump above the water level. The pump must pull water upward from the tank or cistern.
These systems are more sensitive to air leaks.
The vertical distance between the water surface and pump is part of the pump's suction lift. The greater this distance becomes, the harder the pump has to work.
If an above-water pump will not stay primed, inspect the entire suction side.
Possible trouble spots include:
- Loose threaded fittings
- Cracked suction hose
- Damaged seals
- Loose hose clamps
- Leaking unions
- A faulty foot valve
- A faulty check valve
- An intake that is not fully submerged
A very small suction leak may pull air inward without leaking much water outward. That can make the problem difficult to see.
Why Does My Pump Keep Getting Airlocked?
A pump that repeatedly fills with air usually has another problem causing the air to enter.
The Tank Is Running Too Low
Guidance on dry-run protection for a water pump helps assess pressure symptoms associated with air or poor priming.
When the water level drops near the intake, the pump may pull air into the line.
A floating intake can also draw air if it is positioned too close to the surface.
Leave enough usable water above the intake and consider low-water pump protection where appropriate.
There Is a Leak on the Suction Side
Leaks between the tank and pump are one of the most common causes of repeated loss of prime.
Check every connection between the water source and pump.
Because this section may operate under suction, it can pull air through a bad fitting without producing an obvious water leak.
The Check Valve Is Leaking
A check valve allows water to move in one direction.
If it leaks backward after the pump stops, water can drain out of the suction line and be replaced by air.
The next time the pump starts, it may need to be primed again.
A foot valve at the end of a suction pipe serves a similar purpose.
The Suction Line Has High Spots
Air naturally rises.
A suction pipe that goes up, down, and then up again can create places where air collects.
Where practical, suction piping should have a simple route that does not create unnecessary air pockets.
A Filter or Strainer Is Blocked
A dirty filter before the pump can restrict water supply.
The pump may struggle to get enough water and may behave as though it is airlocked.
Clean serviceable strainers and filters according to their instructions.
If the restriction keeps returning, inspect the tank for sediment or debris that may be reaching the intake.
Airlock vs. Cavitation
Airlock and cavitation are not the same problem.
An airlock involves actual trapped air interfering with water flow.
Cavitation happens when pressure at the pump becomes so low that small vapor bubbles form in the water. Those bubbles collapse inside the pump and can cause noise and damage.
Cavitation may be caused by:
- A restricted intake
- A suction pipe that is too small
- Excessive suction lift
- A clogged filter
- Too many fittings
- Insufficient water reaching the pump
A pump that sounds like it contains gravel or marbles should be shut down and investigated rather than allowed to keep running.
What If the Pump Will Not Prime?
If you fill the pump with water but the level quickly disappears, water may be draining backward through the suction system.
Check the foot valve or check valve.
If the pump stays full but still cannot draw water, possible causes include:
- A suction leak
- A clogged intake
- Too much lift between the tank and pump
- A blocked pipe
- An improperly installed valve
- A damaged pump
- Incorrect pump rotation on systems where rotation direction applies
Do not repeatedly run the pump dry while troubleshooting.
Can You Bleed Air From a Pressure Tank System?
Yes, but the pressure tank itself usually is not the place where you manually bleed normal operating air.
Most modern pressure tanks use a sealed air chamber separated from the water by a bladder or diaphragm. That air is needed for the tank to work.
Do not release air from the tank's air valve simply because you hear air in the water lines.
Air coming from faucets normally points to air entering or remaining in the water plumbing.
If the pressure tank is waterlogged, rapidly cycling, or has a damaged bladder, that is a different problem.
Preventing Airlocks in Rainwater Pump Systems
A few design choices can greatly reduce air problems.
Keep the suction pipe:
- Short where practical
- Properly sized for the pump
- Airtight
- Free from unnecessary high points
- Protected from kinks and damage
Also keep the tank intake submerged and maintain strainers, filters, check valves, and fittings.
If your pump can be damaged by dry running, a low-water or dry-run protection device may help shut it off when water is unavailable.
What About Airlocks After Cleaning a Rainwater Tank?
Air problems often appear after a tank, pump, filter, or pipe has been drained for maintenance.
Before restarting:
- Reopen all valves needed for normal flow.
- Confirm the tank contains enough water.
- Fill or prime the pump if its design requires it.
- Open a downstream outlet.
- Restart the pump.
- Let trapped air escape until flow is steady.
- Check for leaks and normal pressure.
Do not assume a pump will automatically reprime after a system has been emptied.
When to Stop Troubleshooting
Turn the system off and get qualified help if:
- The pump trips a breaker repeatedly.
- Electrical parts have become wet.
- You smell burned insulation.
- The motor becomes unusually hot.
- The pump cannot hold prime after obvious leaks are corrected.
- The pressure system behaves unpredictably.
- You suspect pump, motor, pressure switch, or wiring damage.
- You would need to open electrical or pressurized equipment beyond normal user maintenance.
Pump systems combine water, electricity, and sometimes significant pressure. Repairs involving wiring, motor components, or pressure controls are best left to someone qualified for that work.
Frequently Asked Questions
How long should it take to get an airlock out of a water pump?
A properly primed system may clear trapped air within a short period after the pump starts. If the pump continues running without producing steady water, switch it off rather than letting it run dry. A persistent problem often means air is entering through a leak or the pump is not receiving enough water.
Can an airlock damage a water pump?
Yes. An airlock can prevent water from reaching parts of a pump that depend on water for cooling or lubrication. Extended dry running can damage some pumps.
Should I leave a faucet open while priming a pump?
Opening a downstream faucet or outlet can give trapped air somewhere to escape. Once the pump is primed and running, leave the outlet open until the water flow becomes steady.
Why does my rainwater pump lose prime overnight?
Water may be draining backward through a leaking check valve or foot valve. A suction-side air leak can also allow the line to empty. Inspect the suction plumbing rather than simply reprime the pump every day.
Can a blocked filter make a pump seem airlocked?
Yes. A clogged filter or intake strainer can restrict water enough that the pump cannot maintain normal flow. Check and clean serviceable components before assuming trapped air is the only problem.
Does a submersible pump need to be primed?
Normally, no. A submersible pump sits below the water surface, so its pumping section is already surrounded by water. However, air can still become trapped in discharge piping after the system has been drained.
Why does water spit air from the faucet after the pump starts?
Some sputtering is normal after pipes have been emptied. It should stop as the trapped air leaves. If air keeps returning during normal use, inspect the suction side for leaks or a low water level.
