Is Your Submersible Well Pump Losing Flow? 3 Common Causes and Fixes

A sudden drop in flow rate is one of the most common problems with submersible well pumps. However, in most cases, it does not mean the pump needs to be replaced. More than 90% of flow reduction issues are usually caused by the following three factors.

By troubleshooting them step by step, you can often restore normal performance and avoid unnecessary maintenance costs.

Cause 1: Falling Water Level or Low Dynamic Level

When the water level in your well drops below the pump’s intake or its rated operating depth, the pump begins to “suck air” or experience cavitation. This leads to a sharp decrease in output or intermittent water flow.

How to Identify the Problem

1. Listen to the Pump Noise

If the pump produces irregular knocking or gravel-like sounds, cavitation may already be occurring.

2. Measure the Water Level

Use a water level meter or measuring rope to check both the static water level and dynamic water level (while pumping).

If the dynamic water level is close to the pump intake, the low-water-level issue is likely the cause.

Solutions

• Lower the pump an additional 3–5 meters deeper into the well;
• Ensure the pump remains at least 2 meters below the dynamic water level;
• Install a water level controller or electronic float switch to prevent dry running;
• Install a valve on the discharge pipeline to reduce output flow and match the well recovery rate.

Cause 2: Clogged Intake Screen or Impeller

Well water often contains sand, rust, scale, and biological debris. Over time, these materials can clog the inlet screen or block the impeller passages, restricting water intake.

How to Identify the Problem

1. Lower Operating Current

The motor current becomes 10–20% lower than normal due to reduced load.

2. Unstable Outlet Pressure

Pressure gauge readings fluctuate and remain below normal.

3. Intermittent Flow Reduction

Flow starts normally but gradually decreases after several minutes of operation, then recovers later.

Solutions

• Pull the pump out of the well for inspection;
• Clean the inlet screen using a high-pressure washer or steel brush;
• If necessary, disassemble the pump and remove debris from the impeller and diffuser;
• Perform regular maintenance every 6 months;
• Install a pre-filter at the wellhead to reduce contamination.

Cause 3: Mechanical Wear or Electrical Issues

If the water level is fine and there are no clogs, the problem likely lies within the pump’s hardware or the power supply.

A. Worn Impellers or Diffusers

• Symptom: Common in pumps older than 2 years or those operating in “sandy” wells. The flow decreases, but the current remains normal or slightly high. Upon inspection, the impeller edges will appear eroded or pitted.

• Solution: Replace the worn impellers and guide vanes. If the pump housing itself is severely eroded, it is usually more cost-effective to replace the entire unit.

B. Low Voltage or Incorrect Cable Sizing

• Symptom: The pump runs but sounds sluggish (a low-pitched hum). Flow is consistently weak. Testing reveals the voltage is 10% lower than the rated requirement (e.g., less than 207V for a 230V system).

• Solution:

  • Ensure the cable diameter is thick enough for the length of the run (long distances require heavier gauge wire to prevent voltage drop).

  • Check for burnt or pitted contacts in the control box or pressure switch.

Submersible Well Pump Installation Diagram

Summary Checklist