Troubleshooting Pumps: The Pump Turns On, But There’s No Water

What to look for when the pump starts but does not deliver any effluent

Troubleshooting Pumps: The Pump Turns On, But There’s No Water

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When the septic pump starts but does not deliver any effluent, there are two main areas to check: the pump, and the tank or piping. 

Remember, always use caution when working with electricity and turn off power supply breakers when testing components within the electrical system. If you are not 100% confident you can perform any of these tests safely, call a professional.

Pump problems

  • A clogged or damaged impeller. Remove the screen and observe the condition. Clean the impeller and remove any blockage. Products such as hygiene wipes, feminine products and other bathroom trash items could be the problem. Educating the property owner about not flushing these items may be necessarily.  
  • A clogged screen or pump inlet. Examine and observe what is clogging the screen. Clean the screen, and discuss with the owner as needed.
  • The motor is running backward continually. Disconnect the power and remove the pump from the tank. Observe the impeller and shaft rotation. If it’s a single-phase unit, take the pump to an authorized service center for correction. If it’s a three-phase unit, have an electrician reverse the rotation by inverting two of the three power cables.
  • The tank bottom has sludge. There should be little to no sludge in the dosing chamber at the pump intake. Tank cleaning may be needed.  
A pump that has been sitting in and pumping sludge
A pump that has been sitting in and pumping sludge
  • An improperly sized pump. Check the design or code to determine the required pump. The critical aspect to confirm is the total dynamic head — based on the friction loss, elevation difference and the required head at discharge. You may need to consult with the permitting authority, designer or engineer for proper sizing. If it’s found to be too small, replace it with an appropriately sized pump. 
  • An inappropriate electrical supply. Check what phase of power the pump needs (on the pump label/wiring diagram). If it requires three-phase but the electrician ran two-phase power out to the pump, either the wiring or the pump needs to be replaced.

Tank or piping problems

  • Water inflow is excessive. Check the tank for leaks. Check the home or facility for leaking fixtures — toilets, faucets, etc. Confirm that clean-water sources are not connected, particularly footing drains. Also, confirm that the soil treatment area is taking water. If it is fully ponded, effluent may be running back after a dose from downstream components.
  • Pipe discharge is closed by obstruction or ice. Examine and observe. Clean, snake or thaw the discharge line.
  • An inadequate discharge pipe diameter. Measure the discharge pipe and compare with the manufacturer's suggested diameter as it should be no smaller than the pump discharge. You will have to replace the pump or have larger-diameter discharge piping installed.
  • A defective, inoperative check valve or one installed in the wrong direction. Observe the arrow on the check valve indicating direction of flow, and install the check valve in the opposite direction if required. If the check valve is the right direction but still not working properly, look inside the dosing tank after a dose. If there is turbulence at the bottom of the tank, the valve is not working. Examine and clean the check valve. The valves need to open and the problem may be related to air locking the valve, since it needs to release air as the pump starts pushing effluent into the system. Sometimes the built-in small air release becomes plugged, so it may need to be cleaned. You may want to drill a 1/4-inch perforation to eliminate the problem in the future.
  • Too high a static and friction head. If the discharge pipe length is extremely long, the friction losses may exceed pump capacity. Observe the number of pipe fittings and reducing bushings. Remove any reducing pipe fittings and elbows. You probably will need to have a higher-head pump installed and have larger-diameter discharge piping installed.

About the author
Sara Heger, Ph.D., is an engineer, researcher and instructor in the Onsite Sewage Treatment Program in the Water Resources Center at the University of Minnesota. She presents at many local and national training events regarding the design, installation, and management of septic systems and related research. Heger is education chair of the Minnesota Onsite Wastewater Association and the National Onsite Wastewater Recycling Association, and she serves on the NSF International Committee on Wastewater Treatment Systems. Ask Heger questions about septic system maintenance and operation by sending an email to

This article is part of a series on troubleshooting pumps:


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