# Why is my well pump humming but not pumping water? > A well pump that hums but moves no water: a failed capacitor or relay, a locked pump, low voltage or a jet pump that lost prime. Learn what to do. URL: https://wellbornesuffolkwellpumprepair.com/guide/well-pump-humming-not-pumping/ Learn A hum means power is reaching the motor but it cannot turn. The cause is often a small part above ground. A well pump that hums but moves no water is getting power but cannot spin. On three-wire submersibles the usual cause is a failed start capacitor or relay in the control box, which is fixed at ground level. Other causes are a pump locked by sand, low voltage, or a jet pump that has lost its prime. Switch it off; a stalled motor overheats quickly. [Wellborne](https://wellbornesuffolkwellpumprepair.com/) sees a humming, stalled pump most often after a storm or in an older three-wire system. The hum itself is a useful clue: electricity is reaching the motor, but the motor cannot get turning. ## How a submersible starts A single-phase submersible motor needs a boost to start spinning. On a three-wire pump, that boost comes from a **start capacitor** in the [control box](https://wellbornesuffolkwellpumprepair.com/pressure-switch-and-control-box-repair/) on the wall, switched in by a **relay** for a moment at start-up and then dropped out once the motor is running. Two-wire pumps carry similar start components inside the motor. If the capacitor has failed or the relay is stuck, the motor gets running current but no starting boost. It hums, draws high current, and stalls. Its thermal overload may then trip it, and it may try again later, humming each time. ## The common causes **Failed start capacitor or relay.** The most common cause on three-wire pumps, especially after a power surge or lightning nearby, and in older control boxes that have run hot for years. Fixed at ground level by replacing the part, after testing confirms it. **Low voltage.** A pump at the end of a long cable run, on a weak supply, or running from an undersized generator may not get enough voltage to start. It hums instead. **A locked pump.** Sand or silt can jam the impellers, or a bearing can seize. The motor has power but the pump end will not turn. That needs the pump pulled. **A [jet pump](https://wellbornesuffolkwellpumprepair.com/jet-pump-repair/) without prime.** A jet pump that has lost its prime spins but moves [no water](https://wellbornesuffolkwellpumprepair.com/no-water-from-well/), which can sound like a strained hum. The fix is finding the [suction leak](https://wellbornesuffolkwellpumprepair.com/guide/jet-pump-losing-prime/), not replacing the motor. ## What to do right away Switch off the pump’s breaker. A stalled motor overheats fast, and every attempt to start it adds heat. Note where the hum comes from, the control box on the wall or the pump, and whether it happened after a storm or outage. Then leave the testing to someone with meters, because the control box and switch carry line voltage and capacitors can hold a charge after the power is off. ## How it is diagnosed The control box is tested first on three-wire systems: the capacitor’s value, the relay’s operation and the voltage at the box while the pump tries to start. Amp readings on the motor leads show whether it is drawing locked-rotor current. If the box tests good and the motor still draws high current without turning, the pump end is likely locked, and an insulation test confirms the motor windings are intact before the pump is pulled. ## If sand locked the pump A pump jammed with sand usually means the pump is set too close to the bottom of the well, the screen is letting sediment through, or the well is being pumped harder than its yield. Replacing the pump without addressing that brings the same failure back. The pump setting, the well’s yield and its [sediment](https://wellbornesuffolkwellpumprepair.com/guide/sand-and-sediment-in-well-water/) are checked when the pump comes out. ## Two-wire pumps Two-wire submersibles have no control box; their start components are sealed inside the motor. A two-wire pump that hums or will not start usually has a fault in the motor itself, the cable or the supply voltage. Surface tests still come first, but a failed internal starter means the pump has to come up. ## Preventing it A lightning arrester protects the control box from surges. A control box mounted where it stays cool and dry lasts longer. Correct wire size for the depth prevents low-voltage starts. And on deep Suffolk wells, keeping the pump set well above the bottom avoids sand. For help with a stalled pump, call [(757) 919-1972](tel:+17579191972). Related service [Deep submersible repair](https://wellbornesuffolkwellpumprepair.com/submersible-well-pump-repair/) More guides - [A well pump that trips the breaker](https://wellbornesuffolkwellpumprepair.com/guide/well-pump-tripping-breaker/) - [Well pump after a power outage](https://wellbornesuffolkwellpumprepair.com/guide/well-pump-after-power-outage/) - [Jet pump losing prime](https://wellbornesuffolkwellpumprepair.com/guide/jet-pump-losing-prime/) - [Sand and sediment in well water](https://wellbornesuffolkwellpumprepair.com/guide/sand-and-sediment-in-well-water/) ## Questions people ask ### Where is the hum coming from? On a three-wire submersible, often from the control box on the wall, where the relay or capacitor is trying to start the motor. On a jet pump, from the pump motor itself. ### Can I replace the capacitor myself? Capacitors store a charge even with the power off and the control box carries line voltage. It is a job for someone with the right meters, who can confirm the capacitor is the real fault. ### Will the motor be damaged by humming? A stalled motor draws high current and heats quickly. Its thermal overload may trip it, but repeated stalls shorten its life. Switch it off at the breaker until it is checked.