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Prime Spa Pump Purge Air Lock Solved

How to Prime a Hot Tub Pump - Removing Air Locks

My pump is running but there is no water coming out!

Preventing Hot Tub Pump Air Locks

When refilling the spa, it is best to put the hose in the filter compartment. That can help to push some of the air out of the pump.  It is best to avoid the air lock in the first place.  Also assure the filter is clean and the jets are open (adjustable jets can be opened by turning the ring around them in the clockwise direction).

In the case of a mild air lock on startup, it may be enough to turn the pump on high speed and if no success, turn it back to low speed and then back to high speed.   That may work if some bubbles are already coming out of the jets.  Otherwise, it may be time to open the cabinet, locate the main pump/circulation pump and then open the pump union a little in order to let trapped air escape.

Never run the pump without water in it because that could burn up the pump motor.  In order to fix the problem, the pump needs to be primed by either entering priming mode on a newer control system, or run the pump on low speed about 15 seconds and then turn to high speed for about 10-15 seconds, then off. Then cycle through again in the case bubbles are starting to form.  This is the easier way to remove a mild air block /air lock. If this does not work after 3 times, then stop since running a pump dry for more than a short time can damage the pump.  At this point turn off the spa breaker/gfci shutoff and open panel to locate the main pump and purge some air from the pump.

Purging a Spa Pump

loosenunionWhen filling a new spa for the first time, or when refilling a hot tub after a water change, the main pump that circulates water may not be working on either low speed or high speed.  Newer spa control systems have a purge cycle that help the pump get the water moving, but sometimes air gets trapped in the pump and needs to be let out.

If the pump has air trapped in it, do not operate the pump dry for an extended period of time or damage may occur,  but instead have air removed from the system by opening the union nut on the pump slightly to purge the trapped air.

If there are no channel locks available, some techs may use a flat screwdriver and a hammer to get the union nut moving (carefully as the screwdriver can slip causing injury) or use a small wrench to loosen one of the freeze plugs on the wet end - just be careful not to loosen it too much so it does not come off or water will start gushing out.

"Lefty Loosey, Rightey Tightey" - turn left/counterclockwise to open union slightly and right to tighten back up.

Once air is bled out of the line and the union or pump plug closed again, turn breaker back on and set the pump to high speed to complete the purge.

When a Pump Needs to be Purged

If the pump is humming and not moving water, the impeller is spinning but not moving enough water which can be caused by trapped air.

Air can be released from the pump either by slightly opening one of the freeze plugs or bleeder plug on the wet end, or by opening a union nut, preferably the highest one depending on how the wet end is situated.

Just barely open the union nut and hear the air escape, then a little water starts to drip and then retighten the nut.

loosen pump union purge air
Loosening a pump union with large pliers, channel locks or oil filter wrench

For safety, techs recommend turning off the power to the spa, then opening the union nut a little until a hissing sound is heard and some water starts to come out, then re-tighten.  A pair of large pliers or channel locks may be helpful if the nut cannot be turned by hand.  When re-tightening, do not overtighten in order to avoid cracking the union nut.


Fill spa from the filter compartment to reduce chance of air locks when refilling your spa.