Pump sucking air or filter blowing bubbles?

In a standard swimming pool setup the pump pulls the water from the pool and pushes it through the filter and then it will return to the pool or other secondary pumps might push it to a pressure cleaner or through a solar system.

The pipe from the skimmer box to your main pump is where the water gets sucked into the pump from the pool. A break in this line will cause your pool to possibly lose water when switched off but it will also suck air and blow bubbles potentially causing your pump to lose prime or your cleaner to stop.

The pipes from the pump to the filter and from the filter back to the pool contain water at pressure being pushed back into the pool. A break in any of these pipes will leak (and not suck air) and you will lose water when the filter is running. A break in the underground pipes will also leak when the filter is switched off.

Most filters will self-bleed the air out through the return jets by blowing bubbles. If air is accumulating in the filter and possibly draining the pump out when you switch it off your pump will be sucking air but you may not have enough back pressure to bleed the air. This can occur if you have an oversized filter (not a bad thing) or a new clean one so there is no dirt to build up back pressure. The primary problem is still that your pump is sucking air and rectifying this will solve both problems.

Note: Most automatic pool cleaners come with a pressure relief valve or speed control. This valve is important as it ensures your pump gets adequate water flow. If over-tightened or not used your pump may struggle to draw enough water and this will cause it to suck more air. With adjustable valves always loosen them out until the cleaner stops then slowly tighten them until the cleaner starts to move. This is where you should leave the valve. You do not need to adjust it again. If the cleaner stops it will usually mean you need to clean the filter.

Before testing always clean your filter. On sand or d.e. filters it is often better to test on recirculate as this gives you a full flow of water (if this solves the problem you need to clean your filter).

If air is your problem work your way from your pool to your pump. Check the pool cleaner hoses for breaks, try with and without the vacuum plate (use hole at bottom) which will identify a broken skimmer box, check any connections, especially rubber connectors in front of the pump for breaks. Remove, re-align and re-tighten all connections on the suction line. Check that the hair and lint basket in the pump is seated properly and that the lid is sealed with an o-ring.

Any connections in the suction line such as chemical feeders can also cause problems. The easiest way to check your pool hose is to lift it segment by segment out of the water while the cleaner and pool is operating. You will hear a hissing noise wherever there is a hole, or split.

If you have not made any improvements on your air problem you may have a broken pipe underground. If you have a major air problem then an underground break would also cause the pool to lose water. If you believe this is the cause plug the hole in the bottom of the skimmer box with anything you can find (a rag or squash ball or expansion plug etc) and leave your filter switched off. Measure the height of the water and leave the pool for a few days before re-measuring (add chlorine as per normal). If the pool does not lose water you have a broken suction line underground.

With this information a pool serviceman will be able to advise you the best way to rectify the problem.

5 thoughts on “Pump sucking air or filter blowing bubbles?

  1. getting fine air bubbles in pool return lines for 16 minutes then no air bubbles for approximately 14 minutes. This cycle repeats over and over? narrowed it down to filter or heater? what could be causing this

    • Hi. it will be the pump or suction line. Check the lid of the pump and see if any air bubbles are present. if so turn pump of and see if any air bubbles can be seen surfacing. if a suction pool cleaner is connected try without as may be pin hole in hose. The mechanical seal of the pump can also cause this if the pump is above water level. Sometimes a small amount of water may be under the pump. Have system running then turn off and try and see if you can hear air or bubbles in or around the pump. After the pump the system is under pressure so any faults would leak water not suck in air whilst running. My email richard@poolclinic.com.au

  2. Zodiac Sand Filter getting air in when turned off….Ok when running no air bubbles…..as soon as turned off you can hear bubbling at top of filter and then air getting in and water goes down so far in the lint basket…then when pump is switched back on it will push the air back out into the pool and work ok ?

    • Hi.
      It appears that the gasket inside the backwash valve may have failed or the O rings under the handle need replacing.
      If o rings normally water comes out under handle.
      If gasket there will be water leaking down the drain. Undo the union on the waste pipe (single pipe ) and listen when pump is turned off.
      A cheap and simple fix.


      • Hi Richard….thanks for your help…Ok on the Multi-Port I have replaced the handle O rings under the handle..also the top large O ring and the spider gasket..also made sure all pipe fittings are tight.
        But ! sorry to say 10 mins after shut down I can hear bubbling at top of sand filter and then can see bubbles and air going into saltmate cell electrode and then water going down from saltmate cell….then water going down to a certain level in lint basket below ? Any more tips would be appreciated….Cheers,Gerry

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