WiremanWireman · Well pump not running: troubleshooting for electricians · 2023 NEC ·
Well pump not running
Pressure switch, 2-wire or 3-wire control box, running amps, then the motor and drop cable.
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How it works
A pressure switch turns the pump on when pressure falls to its cut-in setting and off at cut-out, commonly 30/50 or 40/60 psi. A 2-wire submersible pump has its start parts inside the motor and runs straight from the pressure switch. A 3-wire pump has a control box above ground with a start capacitor and relay. A pressure tank stores water so the pump doesn’t start for every glass. Pulling the pump out of the well is a job for a well or pump contractor, so finish the electrical diagnosis from the surface first.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What does the pressure gauge show?
- Below cut-in, pump not runningTest: Check the pressure switchExpect: About 240 V on the line side, and the same on the load side when the contacts are closed below cut-in.
- No voltage on the line sideNo power to the pressure switch
- Line good, load side 0 VPressure switch contacts not closing
- Voltage on the load sideIs there a control box between the pressure switch and the well?
- Yes, a control box (3-wire)Test: Test the control box partsExpect: Capacitor within its printed range, and no burned parts.
- Capacitor or relay badFailed control box part
- Box parts test goodTest: Clamp the pump currentExpect: Close to the rated running amps.
- 0 ATest: Test the motor and drop cableExpect: Resistance close to the pump maker’s table for that motor and cable length. OL to ground.
- Open (OL) between leadsOpen motor winding or broken drop cable
- Reads to groundMotor or cable shorted to ground
- Normal readingsStuck pump, failing motor, or low voltage
- Very high, then it tripsStuck pump, failing motor, or low voltage
- Normal amps, no pressurePump runs but doesn’t deliver water
- 0 ATest: Test the motor and drop cableExpect: Resistance close to the pump maker’s table for that motor and cable length. OL to ground.
- No box (2-wire)Test: Clamp the pump currentExpect: Close to the rated running amps.
- 0 ATest: Test the motor and drop cableExpect: Resistance close to the pump maker’s table for that motor and cable length. OL to ground.
- Open (OL) between leadsOpen motor winding or broken drop cable
- Reads to groundMotor or cable shorted to ground
- Normal readingsStuck pump, failing motor, or low voltage
- Very high, then it tripsStuck pump, failing motor, or low voltage
- Normal amps, no pressurePump runs but doesn’t deliver water
- 0 ATest: Test the motor and drop cableExpect: Resistance close to the pump maker’s table for that motor and cable length. OL to ground.
- Yes, a control box (3-wire)Test: Test the control box partsExpect: Capacitor within its printed range, and no burned parts.
- Near 0 psi, pump offLow-pressure cutoff has locked the pump out
- Pump runs but pressure won’t buildPump runs but doesn’t deliver water
- Pump turns on and off rapidlyWaterlogged pressure tank or clogged switch tube
- Below cut-in, pump not runningTest: Check the pressure switchExpect: About 240 V on the line side, and the same on the load side when the contacts are closed below cut-in.