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Troubleshooting Residential (under the counter) RO Systems

Symptom Possible Cause Remedy
No water in storage tank Filter cartridges have failed Replace filter cartridges as indicated
Cartridges upside down Install carbon block filter right side up as indicated on the filter.
No pressure in storage tank Check pressure with gauge.  Refill or reduce pressure to max. 8 psi.
Automatic shut-off malfunctioning Check lines to valve for correct hook-up and check for water running into drain.  Replace if necessary
Kinked lines Straighten lines if necessary
Getting low flow Incoming water pressure too low Check source of feedwater for pressure.  If feed pressure is below 40 PSI, a booster pump is required.
Change in feedwater temperature The RO membrane used in your unit is rated to produce its specified gallons of water per day at 77F (25C) and 60 psi.  Water production production will decrease approximately 1.5% for each degree (F) that your incoming water is below 77F.
Storage tank pressure too low Check pressure with gauge and refill to max. 8 psi
Filters are clogged Replace filters
Water leakage at filter housings Filter sumps are loose Retighten the filter sumps to the caps
Burr on edge of filter housing Remove burr with emory cloth or sand paper
O-Ring in filter bowl is missing, damaged, or not seated properly Replace or position correction
Water backing up to air gap in faucet Line is clogged Clean out the line
Line is too long Must be as short and straight as possible
Drain is clogged Disconnect the drain line and clean out with probe or by flushing
Faucet spout is dripping Handle sticking or worn Replace the faucet assembly

Troubleshooting Residential Booster Pump Systems


  • The pump will not run:
    •  Start at the source to determine where the electrical current flow has been interrupted. Use a multi-meter to check the line voltage, and the transformer output. If the transformer is not functioning properly its current capacity may have been exceeded. Please consult the factory.
    • If the transformer is properly sized, and is delivering the correct voltage to the system, remove the holding tank pressure switch (PSW) from the system by disengaging both connectors, and connecting the pump directly to the transformer.
      • If the pump now runs, the pressure switch is faulty, and needs adjusted or replaced.
      • If the pump still fails to run, the electrical path has been interrupted within the motor, and should be returned to the factory for repair.
  • The flow and/or pressure is too low:
    Most Aquatec boost pumps are designed to limit the maximum output pressure to 110 psi, to protect the membrane and other components from damage. The normal operating pressure as measured after the pump, and before the membrane, will be approximately 80 psi.
    The flow rate of the 6800 series pump during operation is about 500 ml/min. The 8800 is double that flow. If these parameters are not being met, please check the following:
    • 1.Is the pump properly sized to handle the production rate of the membrane, plus the brine flow allowed by the restrictor (usually 4 or 5 times the permeate production)?
    • Is the system receiving adequate feed water? The pumps inlet chamber must be flooded to prevent performance robbing air ingestion into the compression chambers.
    • Debris entering the pump, such as residue from an activated carbon filter
      improperly located on the inlet side of the pump, may restrict the pumping operation. Consult the factory for valve cleaning instructions.
  • The pump will not shut off:
    This is usually caused by a pressure switch that is:
    • Not mounted to properly sense the pressure in the storage tank, or
    • Will not open at a pressure less than the minimum allowed by a hydraulic shut off valve. Check with the supplier of the RO system. If the shut off valve stops the flow of feed water before the storage tank reaches the shut off pressure setting of the switch, the switch will remain closed, and the pump will run continuously. The switch can be adjusted to open at a lower pressure, or may be replaced by a 40 psi PSW.
  • The pump operation is too noisy:
    Boost pumps operate at relatively slow speeds, accounting for their quiet operation. Pumps that exceed expected noise levels usually have one of the following problems:
    • Entrapped air (which will eventually dissipate). Make sure air is not being drawn into the pump.
    • Water may have damaged the bearings, or other motor components. Check for internal leaks, as well as water entering the motor from an external source.
    • Squeaking may be associated with the by-pass mechanism; brush contact with the commutator surface; or inadequate lubrication in the rear bearing. Consult the factory.

  • The pump is causing electrical noise interference:
    • Try locating the pump on a dedicated electrical circuit, separate from the device that is being interfered with.
    • Consult factory for pumps available with electronic noise suppression.


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All Content on this site is  intended for informational purposes for experienced water treatment professionals only.  Applied Membranes, Inc. does not assume any liability for any damages caused by the misapplication or misinterpretation of any of the information contained on this website.
Applied Membranes, Inc. 2007