My Submersible Pump Sounds Rough and Has Low Water Flow

1. Check the Pump’s Running Speed

If a pump is not running at the correct speed, it can cause cavitation. This occurs when:

• A pump is running at a high speed, and the water source cannot replenish itself quickly enough. This causes the pump to suck air in place of water.
• A pump is running at a low speed and cannot push water to the intended destination. This causes the water to churn inside the pump creating air pockets.

 

In the middle of the day and in good light conditions, look at the Speed Control dial located on the centre right of the controller’s circuit board.

 

1a. Cavitation at Full Speed:

If the dial is at 10 (full speed) the water source may be having trouble replenishing the water quickly enough.

Turn down the speed from 10 to 5 and check if the pump is still running rough:

• If it is, reduce the speed further bit by bit and recheck each time.
• Once the pump is no longer pumping water faster than the water source can replenish it, allow the pump to run for 1 – 2 hours to push the air out of the pump.
• Once the air is out of the pump and it is no longer running rough, slowly turn the speed up being careful to not allow the pump to pump faster than the water can be replenished.

 

1b. Cavitation at low speed:

If the dial is not on 10 (full speed) the pump may be having trouble getting water to the intended destination.

Turn up the speed to 10 and check if the pump is still running rough:

• If the pump stops running rough, confirm that water is getting to the intended destination.
• If the pump continues to run rough, proceed to the next step.

 

2. Is the Pump Fully Submerged?

Submersible pumps need to be well below the water’s surface to ensure a steady intake. If the pump isn’t deep enough in the bore or tank it may be sucking in air and causing:

• Cavitation which creates noisy operation, low flow and lack of pressure.

Make sure the pump is completely underwater. This includes the inlet for the pump’s power cable.

• Check the pump inlet screen for debris or blockages and clean it if needed.
• If the pump is fully submerged and there are no signs of debris or blockages, proceed to the next step.

 

3. Inspect the Low Water Sensor Placement

If the sensor is installed too low or incorrectly, it will not protect the pump from running dry. This can cause damage to the pump and make it noisy as it runs. Ensure that:

• The sensor is mounted vertically, with the wire exiting from the top.
• It is positioned at least 1 metre above the water inlet.

 

4. Check the Inlet for Debris and/or Blockages

Sometimes the issue is as simple as debris stuck in the intake. Stop the pump from running by turning off the solar isolator and remove the pump from the water source. With the pump stopped and removed check:

• The inlet screen for debris such as grass, dirt, or plastic wrapping.
• If installed in a bore, ensure the pump is not drawing in mud or grit from the bottom.
• Clean it if needed, reinstall in the water source, turn the solar isolator on and run the pump to test its operation.
• If the pump is fully submerged and there are no signs of debris or blockages, proceed to the next step.

 

5. Check for Airlocks in the Pipeline

Air trapped in your pipework can block flow entirely. This happens when air is stuck in the line (e.g. high point or bend) and the high flow rate of the water compress the air and prevents water from flowing past it.

Running your pump at a slower flow rate can slowly push the air out, but you can also:

• Tilt or lift the pipe slightly to let trapped air escape.
• You can also loosen a fitting at a point in the line where air might be trapped, allowing it to hiss out until water flows.

Once the air is purged, the water will flow normally.

 

6. Check Solar Panel Performance
Over time, solar panels can lose efficiency due to connections becoming loose, dirt building up, shading, etc.

• Inspect your solar panels to ensure that they are:
  • Clean and free from dust, bird droppings, leaves, grime, etc. Clean panels gently with a soft brush, a cloth and water if needed.
  • Not shaded — even partial shading on one panel can cause a significant drop in the performance of the whole array.
• The connections are securely connected to each other and not damaged.

• Use a multimeter to check the voltage at the controller:
  • Set you multimeter to detect DC voltage.
  • Place the red (positive) probe on P+ and the black (negative) probe on P- terminals.
    • 24V pump systems should show 35V–55V open circuit voltage (Voc)

• 48V pump systems should show 65V–109V (Voc)
• 72V pump systems should show 80V–140V (Voc)

If voltage is too low, clean the panels and recheck voltage at the P+ and P- terminals.

 

7. Check Motor Wiring (UVW Terminals)

Incorrect or loose wiring between the controller and pump can cause the pump to run rough over time. Check that the motor’s power cable wires are connected to the U, V, and W terminals according to the labels on the wires.

Do not copy any previous installations or colour matching. If you are unsure, compare the labels on the individual wires and the labels of the pump controller’s terminals. You can also refer to the installation guide in the user manual.

• Open the controller and ensure wires are in the correct order based on labels.
• Check that the wires are securely connected to the UVW terminals.
• Look for signs of:
  • Loose wires
  • Burnt terminals, connections, or wires
  • Corroded terminals, connections, or wires
  • Tighten any loose terminals and reseat wires if needed.

 

8. Impeller Wear and Clogging Over Time

Sometimes the issue is as simple as debris stuck in the intake.

• Inspect the inlet screen for grass, dirt, or plastic wrapping and ensure the pump is not drawing in mud or grit from the bottom of the water source.

8a. Submersible Screw/Helical Rotor Pumps (e.g. bore pumps):

These pumps contain a rotor (metal screw) and a stator (rubber sleeve) that wear out over time.

• The rotor and stator (impeller) should be replaced every 1–2 years depending on your local water conditions (e.g. grit or mineral content).
• Remove the pump and check:
  • That the rotor can turn freely inside the stator.
  • It should not feel loose (worn out) or too tight (swollen or hardened rubber). It should turn easily with a firm but gentle grip.
• Rotor and stator should always be replaced as a pair, as they are a matched set.

For instructions, refer to the "How to Replace an Impeller" section of the user manual.

8b. Submersible Centrifugal Multistage Pumps

These pumps have multiple spinning impellers and are sensitive to clogging.

• Check the inlet screen and impellers for blockages (grass, grit, algae, etc.).
• Running the pump backwards can help clean out the impellers if they are not badly clogged.
  • Run the pump backwards for 5–10 minutes.
  • Switch back to forward for 5–10 minutes.
  • Then reverse again one more time.

To reverse the pump’s running direction:

1. Turn the solar isolator off.
2. Open the controller and take a photo of the pump’s power cable wiring.
3. Swap the wires on the V and W terminals with each other.
4. Turn the solar isolator on.

Note: Be cautious and contact Commodore Australia if you are unsure of this process.

If the impellers remain clogged, you may need to disassemble and clean the pump.

• This involves removing and reassembling multiple internal parts in the correct order.

• Contact Commodore Australia on 1300 669 256 for detailed guidance.

 

9. Check for Mechanical Damage

Most pumps have the same mechanical concerns that are common to all types (failed bearings, failed seals, damaged impellers, etc.) however, each type of pump can have specific mechanical concerns depending on their type.

9a. Submersible Screw/Helical Rotor Pumps (e.g. bore pumps):

The most common fault for these pumps is the impeller becoming worn out or damaged, however other faults can include failed seals and/or bearings.

• Remove the pump from the water and check:
  • That the motor shaft can turn freely with a clunking sensation as it is turned. The clunking sensation is the motor shaft’s magnets moving between the windings and is normal.
  • That the motor shaft does not wobble side to side.
  • That the seal where the motor shaft comes out of the motor is clean and in good condition.
  • That the base of the motor is clean and in good condition.
  • That the power cable is not damaged where it enters the impeller housing.
  • That the power cable is not damaged along the length that runs through the impeller housing.
  • That the power cable is not damaged where it enters the motor.

 

9b. Submersible Centrifugal Multistage Pumps

The most common fault for these pumps is the motor shaft and impeller coupling having become worn or stripped over time.

• Remove the pump from the water or disconnect the water inlet pipe and separate the motor from the pump to check:
  • For wear on the motor shaft spline.
  • For wear on the impeller shaft coupling.
• While separated also check:
  • That the motor shaft can turn freely with a clunking sensation as it is turned. The clunking sensation is the motor shaft’s magnets moving between the windings and is normal.
  • That the motor shaft does not wobble side to side.
  • That the seal where the motor shaft comes out of the motor is clean and in good condition.
  • That the base of the motor is clean and in good condition.
  • That the power cable is not damaged where it enters the cable guide.
  • That the power cable is not damaged where it enters the motor.

 

Conclusion:

Main causes of rough running and low water flow include:

• Cavitation due to low water, low/high running speeds.
• Air locks and blockages to inlet, outlet, or pipeline.
• Incorrect wiring or voltage drop.
• Internal wear: impellers, motor spline/coupling, bearings, etc.

Routine inspection every 6–12 months can catch these issues early and keep your pump running smoothly. If in doubt, contact Commodore Australia’s Technical Support team for further assistance.

Phone 1300 669 256 or email support@commodoreaustralia.com.au