As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties.
If your water pump is running but not moving water, sputtering, or losing pressure, trapped air may be the problem. “Bleeding” a pump means letting that air escape so the pump and water line can fill properly with water.
For many surface-mounted pumps, bleeding and priming are closely related. Priming means filling the pump casing and suction line with water before the pump runs. A submersible pump usually does not need manual priming because it sits in the water.
Before You Bleed the Pump
Turn off power to the pump before opening any plug, valve, or fitting.
Also check that the water source has enough water. Bleeding will not fix a pump that is drawing from an empty rain barrel, IBC tote, cistern, or well.
Look for obvious problems such as:
- A closed inlet or outlet valve
- A clogged screen or filter
- A kinked hose
- A loose suction fitting
- A damaged suction hose
- A leaking pipe connection
- A pump mounted too high above the water source
Air often enters through a leak on the suction side of the system. You may not see water leaking out because the pump can pull air inward instead.
How to Bleed a Typical Surface Water Pump
The exact procedure depends on the pump, so follow the manufacturer's instructions when available. For many centrifugal, garden, transfer, and shallow-well pumps, the general process is similar.
1. Turn Off the Pump
Disconnect electrical power before opening the system.
Do not loosen fittings while the pump is running or while a pressurized system is still under pressure.
2. Relieve Water Pressure
Open a faucet, hose bib, or irrigation valve downstream from the pump.
Let the pressure fall before removing a priming plug or opening a bleed valve.
If your system has a pressure gauge, wait until the pressure has dropped.
3. Find the Priming or Bleed Opening
Many surface pumps have a threaded plug near the top of the pump housing.
This may be called a:
- Priming plug
- Fill plug
- Vent plug
- Bleed screw
Do not remove a plug unless you are sure what it does. Some pump fittings should not be opened by the user.
4. Fill the Pump With Water
Remove the priming plug and slowly add clean water until the pump casing remains full.
On systems with a long suction pipe, you may need more water because you are filling part of the suction line as well.
If the water level quickly disappears, there may be a problem with the foot valve, check valve, or suction plumbing.
5. Let Trapped Air Escape
Leave the priming opening loose or open as directed by the pump manufacturer while filling.
Air bubbles may escape as water enters.
Continue adding water until the pump stays full and large air bubbles stop appearing.
6. Reinstall the Plug
Replace the priming or bleed plug securely.
Do not overtighten plastic plugs or plastic pump housings. Excess force can crack the threads or housing.
7. Open the Discharge Side
Make sure water has somewhere to go when the pump starts.
Leaving a faucet or hose valve partly open can help remaining air move out of the discharge line.
8. Restore Power
Turn the pump on and watch its operation.
Water may sputter briefly while remaining air leaves the pipes. Flow should then become steady.
Do not allow a pump that requires water for cooling and lubrication to run dry for an extended period. If it does not begin moving water within the time allowed by its manufacturer, shut it off and investigate the cause.
How to Bleed a Rainwater Pump System
A rain barrel, IBC tote, or cistern system often develops air problems when the storage tank runs low or when suction plumbing is opened for maintenance.
Check the system from the tank toward the pump.
Make Sure the Pump Inlet Has Water
The tank outlet must be submerged and supplying water.
If the pump is above the tank water level, it has to lift water through the suction pipe. This vertical distance is part of the pump's suction lift.
A surface pump cannot pull water from unlimited depth. Excessive lift makes priming difficult and can prevent the pump from working correctly.
Check the Tank Valve
Make sure the valve between the storage tank and pump is fully open.
A partly closed valve can restrict flow and sometimes make pump problems look like trapped air.
Check Suction Connections
Inspect:
- Hose clamps
- Threaded fittings
- Bulkhead fittings
- Unions
- Filter housings
- Pump inlet connections
A bulkhead fitting is a sealed fitting that passes through the wall of a tank.
Even a small air leak before the pump can cause poor priming.
Check the Suction Filter
A dirty screen or filter can restrict water entering the pump.
Clean it according to its instructions before repeatedly trying to prime the pump.
Do Submersible Pumps Need Bleeding?
With causes of weak water-pump output, you can verify pump capacity before continuous use begins.
Usually not.
A submersible pump operates while surrounded by water, so the pump itself normally stays flooded.
If a submersible system is sputtering air, the problem may instead be:
- The water level is too low
- The pump is drawing a vortex from the surface
- A pipe connection is leaking
- Air remains in newly installed discharge plumbing
- A check valve is not working correctly
Do not pull a pump from a cistern, tank, or well without considering electrical safety, lifting weight, access, and confined-space hazards.
Never enter a cistern or enclosed water-storage tank to service a pump unless the work is being handled under appropriate confined-space procedures.
What About Booster Pumps?
Many household booster pumps are designed to operate with a flooded inlet. This means water reaches the pump naturally rather than being pulled upward through an empty suction pipe.
After plumbing work, air can remain inside the pump or pipes.
A common approach is to:
- Turn off power.
- Restore the incoming water supply.
- Open a nearby outlet.
- Use the manufacturer's vent or bleed point if provided.
- Allow water to push the trapped air out.
- Close the bleed point after a steady stream of water appears.
- Restore power.
Automatic booster pumps can have electronic controls, pressure sensors, and dry-run protection. Do not open electrical parts or alter control settings just to solve an air problem.
Why Does My Pump Keep Getting Air in It?
If you have to bleed or prime the pump repeatedly, trapped air is probably a symptom rather than the main problem.
Common causes include the following.
A Suction-Side Air Leak
This is one of the most common causes.
Check every fitting between the water source and pump.
A Bad Foot Valve or Check Valve
A check valve allows water to travel in one direction.
A foot valve is a type of check valve normally installed near the submerged end of a suction pipe.
If it leaks backward, the suction line can drain whenever the pump shuts off. You then have to prime the system again.
A Low Water Level
If the storage tank gets too low, the inlet can begin pulling air.
A floating intake or properly positioned tank outlet can help keep the inlet submerged, but the arrangement must match the intended system design.
Excessive Suction Lift
A pump that is too far above the water surface may struggle to lift water.
The important measurement is the vertical distance between the pump and the actual water level, not simply the total hose length.
Restricted Plumbing
Dirty filters, clogged screens, undersized hoses, and collapsed suction hoses can interfere with priming and flow.
Loose Filter Housing
If a pre-pump filter has been cleaned recently, check its gasket and housing.
A poorly seated O-ring can allow air into the suction line.
How Do I Know When the Air Is Gone?
A properly operating system usually has:
- A steady stream of water
- Little or no sputtering
- Stable pump sound
- Normal pressure
- No repeated loss of prime after shutdown
A few bubbles after opening plumbing can be normal. Continuous bubbles are more likely to indicate an air leak or low water level.
Do Not Keep Running a Dry Pump
Many surface pumps depend on water inside the pump for cooling, lubrication, or both.
Running one dry can damage seals and other internal parts.
If the pump does not establish flow after proper priming, shut it off rather than repeatedly letting it run.
Investigate the water supply, suction plumbing, valves, filters, and check valve first.
When to Call a Professional
Stop troubleshooting and use a qualified pump or plumbing professional if:
- The pump repeatedly loses prime and you cannot find the leak
- Electrical components have been exposed to water
- The motor trips a breaker
- The pump hums but will not start
- The pressure tank or pressure controls appear damaged
- Water leaks from the pump shaft or motor area
- The system operates at unfamiliar or high pressure
- Service requires entering a cistern or confined space
- Underground suction plumbing may be leaking
Pump problems involving household plumbing can also affect water pressure and other equipment, so repeated loss of prime should not be ignored.
Frequently Asked Questions
Is bleeding a water pump the same as priming it?
Not exactly. Bleeding removes trapped air. Priming fills a pump and, in some systems, the suction line with water. On many surface pumps, the two jobs happen at the same time.
Can I bleed a pump while it is running?
Only if the manufacturer specifically provides a bleed valve designed for that procedure. Otherwise, shut off power and relieve pressure before opening fittings or plugs.
Why does my pump work after priming but lose water again later?
The suction line may be draining backward through a leaking check valve or foot valve. A suction-side fitting may also be allowing air into the system.
Why is my pump making noise but not pumping water?
Possible causes include loss of prime, an empty water source, a closed valve, a clogged inlet, excessive suction lift, an air leak, or a mechanical pump problem. Shut the pump off if it is running without water.
Why does water sputter from the faucet after I bleed the pump?
Some remaining air may still be moving through the discharge pipes. Brief sputtering can be normal after priming. Persistent sputtering suggests that air is continuing to enter the system.
Does a rain barrel pump need to be primed?
A surface-mounted rain barrel pump may need priming, especially if it sits above the water level. A submersible pump generally does not need manual priming because it operates underwater.
Can a dirty filter cause a pump to lose prime?
A severely restricted filter can reduce water flow and contribute to poor pump operation. A loose filter housing or damaged seal on the suction side can also allow air into the system.
