Vertical pressure tank connected to a water pump outdoors
Generic photo: W.carter · CC BY-SA 4.0

Well pump hums, won't start or trips overload: control box test (3-wire)

On a 3-wire submersible, the start capacitor and relay in the control box are the most common surface failures and can be tested with a meter. First confirm power through the pressure switch, then test the box. If the box is good or the system is 2-wire, the problem is down the well and goes to a well contractor.

Cross-checked ~60 min advancedBrands: Franklin Electric, Goulds, Grundfos, Others

Before you start

  • 240 V high-current circuit: lock out the breaker and verify dead before opening boxes
  • Discharge capacitors before touching
  • Live voltage/amp checks only with insulated probes and dry footing
  • Stop resetting a breaker that trips instantly

Diagnostic steps

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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

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Well pump hums, won't start or trips overload: control box test (3-wire) · OnCall Tech