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Bleeding air out of a water pump usually means removing trapped air from the pump housing and suction line so the pump can move water normally. On many centrifugal pumps, this is done by shutting off power, opening the priming or vent plug, filling the pump with water, and letting trapped air escape before restarting it.
The exact method depends on the pump. A shallow-well jet pump, garden transfer pump, booster pump, and submersible well pump do not all bleed air the same way.
Why Air Gets Trapped in a Water Pump
Most water pumps are designed to move water, not large pockets of air. If air enters the pump or suction pipe, the pump may lose its prime.
The prime is the water that fills the pump housing and suction line before the pump starts moving water.
Air commonly gets into a pump after:
- The system has been drained.
- A tank or pipe has been disconnected.
- A filter housing has been opened.
- The pump has been replaced or serviced.
- The water source dropped below the suction pipe.
- A suction-side fitting is leaking.
- A foot valve or check valve is not holding water.
- The pump has been allowed to run dry.
A small amount of air in household plumbing may clear on its own through an open faucet. Air trapped inside a centrifugal pump often requires priming.
How to Bleed Air From a Centrifugal Water Pump
The following method works for many surface-mounted centrifugal, jet, and transfer pumps that have a priming or vent opening.
1. Turn Off the Pump
Disconnect electrical power before opening the pump or removing any plug.
Do not loosen a priming plug while the pump is running.
If the pump is part of a pressurized system, relieve the water pressure first. Opening a faucet may help, but follow the pump manufacturer's instructions for your system.
2. Find the Priming or Vent Plug
Look near the top of the pump housing.
Many centrifugal pumps have a threaded plug that allows you to:
- Add priming water.
- Release trapped air.
- Check whether the pump housing is full.
Do not confuse this with a drain plug near the bottom of the housing.
3. Slowly Open the Plug
Loosen the plug carefully.
If the system still has pressure, water or air may escape.
Wait until pressure has been relieved before fully removing the plug.
4. Fill the Pump With Water
Pour clean water into the priming opening until the pump housing remains full.
You may need to wait several seconds while water moves into the suction pipe and trapped air rises out.
Add more water as the level drops.
A pump that repeatedly empties while you are filling it may have a leaking foot valve, check valve, suction pipe, or fitting.
5. Reinstall the Priming Plug
Once the pump remains full, reinstall the plug.
Make sure its seal or thread treatment is appropriate for the fitting. Do not overtighten a plastic pump housing or plastic plug.
6. Open an Outlet
Open a faucet, hose bib, or other outlet on the discharge side.
This gives remaining air somewhere to escape when the pump starts.
7. Restore Power
Turn the pump on and watch its operation.
Water may initially spit or surge from the open outlet as air leaves the system.
Once you have a steady stream of water, close the outlet as appropriate for the system.
Do not let a pump run for an extended period without water flowing through it. Many pumps can be damaged by dry running.
What If the Pump Does Not Pick Up Water?
If the pump still will not move water after being filled and restarted, turn it off rather than allowing it to continue running dry.
Prime it again according to the manufacturer's instructions.
If the problem keeps returning, trapped air may be a symptom rather than the main problem.
Common causes include:
- Suction-side air leak.
- Loose pipe fitting.
- Cracked suction hose.
- Damaged gasket or O-ring.
- Clogged intake screen.
- Failed foot valve.
- Leaking check valve.
- Water source below the intake.
- Suction lift greater than the pump can handle.
- Blocked suction pipe.
- Incorrect valve position.
The suction side of a pump can pull air through a small leak without necessarily leaking much water outward. That can make suction leaks difficult to spot.
Bleeding Air From a Well Pump System
The procedure depends heavily on the type of well pump.
Shallow-Well Jet Pump
A shallow-well jet pump is normally located above ground.
It usually must be filled with water before it can create enough suction to lift water from the well.
If it loses prime:
- Shut off power.
- Relieve system pressure.
- Open the pump's priming port.
- Fill the pump and suction piping as directed by the manufacturer.
- Reinstall the plug.
- Open a nearby faucet.
- Restart the pump.
- Allow air to leave through the faucet until the flow becomes steady.
If the pump repeatedly loses prime, inspect the suction system and foot or check valve rather than repeatedly adding water.
Deep-Well Jet Pump
Deep-well jet systems can be more difficult to prime because they use two pipes and a jet assembly in the well.
Follow the pump manufacturer's priming procedure. Persistent priming problems may require a well or pump professional.
Submersible Well Pump
A submersible pump sits underwater in the well and generally does not need to be manually primed like an above-ground centrifugal pump.
If air is coming from household faucets, possible causes include:
- Work was recently performed on the plumbing.
- The pressure tank or piping was drained.
- The well water level is dropping too low.
- The pump is drawing air.
- There is a leak or equipment problem.
After routine plumbing work, opening faucets may allow normal trapped air to escape.
If air continues returning without recent plumbing work, have the well and pump system checked.
How to Bleed Air From Household Water Lines
Sometimes the pump is working correctly and the air is only trapped in the pipes.
After plumbing repairs or system draining:
- Make sure the water supply is restored.
- Open faucets gradually.
- Allow each outlet to run until sputtering stops.
- Flush toilets and operate other water outlets as needed.
- Check the system for leaks.
Avoid rapidly cycling the pump on and off while doing this.
Regarding air-related water-pump problems, verify capacity margins for reliable long-duration service.
If the system includes water heaters, filters, treatment equipment, or specialty plumbing, follow their startup instructions as well.
How to Bleed a Booster Pump
Many household booster pumps are installed in plumbing that normally stays filled with water.
If one has been drained, the pump may need to be refilled before startup.
Some booster pumps have an air vent. Others rely on opening a fixture while the system refills.
Before restarting a drained booster pump:
- Confirm the inlet water supply is available.
- Open all required isolation valves.
- Make sure the pump housing is full if the manufacturer requires priming.
- Open an outlet so air can escape.
- Do not operate the pump dry.
Automatic booster systems may have special startup procedures, so check the manual before removing plugs or opening the pump.
Why the Pump Keeps Getting Air in It
Bleeding a pump should not normally be a frequent job.
If air keeps returning, look for the source.
Suction Leak
A loose threaded joint, cracked pipe, damaged hose, or worn seal can allow air into the suction line.
This is especially common with above-ground pumps pulling water from:
- Rainwater tanks.
- Cisterns.
- IBC totes.
- Wells.
- Ponds.
- Storage barrels.
Bad Foot Valve or Check Valve
A check valve allows water to move in one direction.
A foot valve is a type of check valve usually installed near the end of a suction pipe.
If the valve leaks, water can drain backward when the pump stops. Air then replaces the lost water, and the pump loses its prime.
Low Water Level
The intake must stay underwater.
A rainwater tank or cistern can become low enough that the pump begins pulling air instead of water.
A floating intake can also draw air if it sits too close to the surface.
Excessive Suction Lift
Suction lift is the vertical distance a surface pump must pull water upward.
Every pump has limits. Long suction pipes, small pipes, restrictive fittings, and vertical lift all make it harder for the pump to draw water.
If the installation exceeds the pump's limits, repeated priming may not solve the underlying problem.
Clogged Suction Line
Leaves, sediment, algae, or debris can restrict an intake screen or suction pipe.
The restriction can prevent the pump from receiving enough water even though the housing is primed.
Bleeding Air From a Rainwater Pump System
Rainwater systems often develop air problems when the storage tank gets low or when a filter or pump is serviced.
Check the whole path from storage to pump:
Tank → intake → suction pipe → valve → filter → pump
Any leak or blockage before the pump can affect priming.
A few installation details can make a big difference.
Keep suction piping:
- Airtight.
- As short and direct as practical.
- Properly sized for the pump.
- Free of unnecessary high points where air can collect.
- Equipped with suitable valves and fittings.
If a filter is installed on the suction side, make sure its housing and gasket seal correctly. A loose filter housing can admit air even when no obvious water leak is visible.
Do Not Confuse Pump Air With Pressure Tank Air
A well pressure tank intentionally contains compressed air.
That air provides the cushion that allows the tank to store water under pressure.
Do not try to bleed all of the air from a pressure tank.
If a pressure tank is waterlogged, short-cycling, or has an incorrect air charge, it requires a different troubleshooting process.
The air trapped inside a pump housing or plumbing line is not the same as the controlled air charge inside a pressure tank.
Signs That the Pump Is Properly Primed
A properly operating pump should generally:
- Produce a steady water flow.
- Build normal system pressure.
- Stop sputtering air after startup.
- Run without unusual grinding or cavitation noises.
- Hold its prime after shutting down.
If water flow disappears again shortly after the pump stops, check the suction line and check valve.
When to Stop Troubleshooting
Turn the pump off if:
- It cannot establish water flow.
- It is running dry.
- It becomes unusually hot.
- It repeatedly loses prime.
- Electrical parts have been exposed to water.
- You find damaged wiring.
- The pressure system behaves unpredictably.
- You cannot safely relieve pressure before opening it.
Electrical work, well servicing, sealed pump repairs, and major pressure-system problems are better handled by a qualified pump, well, or plumbing professional.
Frequently Asked Questions
How long does it take to bleed air out of a water pump?
If the pump only contains a small amount of trapped air, it may clear shortly after the pump is properly primed and an outlet is opened. A pump that will not establish steady water flow after repeated correct priming may have a suction leak, bad check valve, low water source, or another problem.
Can I run the pump with the priming plug removed?
Do not do this unless the pump manufacturer specifically calls for it. Removing plugs from a running or pressurized pump can release water unexpectedly and may allow the pump to lose prime.
Why does my water pump keep losing its prime?
Common causes include a suction-side air leak, leaking foot valve, bad check valve, low water level, cracked suction pipe, or a connection that is not airtight.
Will opening a faucet remove air from the pump?
Opening a faucet helps trapped air leave the discharge plumbing, but it may not prime an empty centrifugal pump. If the pump housing or suction line is full of air, the pump may need to be manually filled first.
Does a submersible pump need to be bled?
Usually not in the same way as an above-ground centrifugal pump. A submersible pump operates underwater. Air at the faucets may instead come from drained plumbing, low well water, or another system problem.
Why does my pump sound like it is pumping gravel?
A rattling or gravel-like sound can be a sign of cavitation, which happens when the pump is not receiving water properly. Stop the pump and check for low water level, blocked suction piping, excessive suction lift, closed valves, or air leaks.
Can a pump be damaged by trapped air?
Yes. Many water pumps depend on water for cooling and lubrication. Running one without enough water can damage seals or other components. Follow the manufacturer's dry-run limits and shut the pump off if it fails to establish flow.
