Sump Pump Humming But Not Pumping Water
Safety first
Some checks below are safe for a homeowner, but others are not. Follow each step’s guidance, and stop if you are unsure or if a step involves gas, high voltage, refrigerant, or pressurized water.
Quick Answer
A sump pump that hums but does not move water means the motor is receiving power but the pumping mechanism is blocked or stalled. The most common causes are a debris-jammed impeller, a float stuck in the "on" position with no actual water to move, a frozen or clogged discharge line, an airlock in the discharge pipe, or a check valve that has seized closed. The motor will burn out quickly if the blockage is not cleared. Always cut power before any hands-on inspection— water and electricity together require extreme caution.
Common symptoms
| Symptom | Possible cause | Safe next check | When to call a pro |
|---|---|---|---|
| Pump hums constantly but pit water level keeps rising | Impeller jammed with gravel or debris—motor runs but cannot spin the impeller | Cut power, remove pump from pit, inspect and clear the impeller and inlet screen | If impeller is broken or housing is cracked; if motor trips breaker repeatedly |
| Pump hums and pit is dry (no water present) | Float stuck in the "on" position with nothing to pump—dry running damages the seal | Cut power, reposition the float so it rests at the bottom; restore power and test with a bucket of water | If float adjustment is not possible or switch is integrated and non-adjustable |
| Pump hums, water level drops slightly then rises again | Partial impeller obstruction or discharge line restriction limiting flow rate | Confirm discharge line exit is clear; check for partial ice blockage in cold weather | If obstruction cannot be cleared from the exterior or discharge line needs replacement |
| Pump hums then trips the circuit breaker | Locked-rotor condition from jammed impeller drawing excess current | Do not reset the breaker repeatedly—this can damage the motor; clear the blockage first | If the pump trips the breaker after clearing debris, the motor winding may be damaged |
| Pump ran fine, stopped working in freezing weather | Discharge line frozen solid—no outlet for water even if pump runs | Confirm exterior discharge exit; check for ice at the pipe end or in an uninsulated run through a cold space | If the line has burst from ice expansion or the freeze recurs each winter (pipe routing may need correction) |
Most common causes
When the pump hums, the motor is alive and receiving power. The problem is downstream of the motor: something is preventing the impeller from spinning freely or water from having a path out.
- Jammed impeller (most common cause of hum-no-pump). The impeller is the spinning component that draws water in and pushes it up the discharge pipe. Fine gravel, pebbles, or debris that enters through the inlet screen can wedge between the impeller and the housing. The motor hums at full power trying to spin against the blockage—but nothing moves.
- Float stuck in the "on" position with an empty pit. If the float is jammed high, the pump runs even when the pit is dry. With no water to cool the motor or move, you hear a hum and the pump generates heat instead of flow.
- Frozen or clogged discharge line. In cold climates, the section of discharge pipe that passes through an unheated space or exits at grade level can freeze solid. The pump hums against the pressure of a closed line and moves nothing.
- Airlock in the discharge pipe. A trapped air pocket at the top of the discharge pipe can prevent priming. This typically happens after the pump has been installed or moved. A properly placed weep hole above the pump prevents this.
- Check valve seized closed. A check valve that has failed in the closed position blocks flow entirely. The pump strains against it and hums loudly.
- Failed start capacitor. On some pump motors, a capacitor assists with startup torque. A failed capacitor can result in a motor that hums at low torque but cannot develop enough force to spin the impeller up to speed. This is a repair for a service technician.
Safe troubleshooting steps
Safety first: sump pits combine standing water with electrical equipment. Follow this sequence carefully.
- Cut power at the outlet before touching anything. Unplug the pump. If it is hard-wired, trip the dedicated circuit breaker. Confirm power is off before reaching into the pit.
- Check whether the pit has water. If the pit is dry, the float is stuck "on." Reposition it so it rests freely at the bottom, then test by pouring two or three gallons of water into the pit and restoring power.
- Check the discharge exit outside. Before removing the pump, go outdoors and confirm the pipe exit is clear and not iced over. In freezing weather, feel for ice at the outlet or in any uninsulated section of line.
- Remove the pump and inspect the inlet and impeller. With power confirmed off, lift the pump out of the pit. Inspect the inlet screen at the bottom for debris. If the pump design allows access to the impeller (check your manual), clear any obstructions by hand or with a non-metallic probe.
- Inspect the check valve. With the pump removed, you can usually push on the check valve flap from below. It should open freely with light pressure. A valve that will not open at all has seized.
- Test before reinstalling. With the pump out of the pit and resting safely on the floor, briefly restore power and observe whether the impeller spins freely (you may hear a change in tone and feel vibration). Cut power again, then reinstall.
Stop and get help immediately if…
There is standing water touching any electrical outlet, extension cord, junction box, or the breaker panel. Do not enter a flooded space with active electricity. Shut off power at the main panel from a dry location and call a licensed electrician. Sump pump repairs should never be performed with the pump plugged in or the circuit live.
When to call a professional
Call a licensed plumber or pump technician if:
- Clearing the impeller does not restore normal operation.
- The pump trips the circuit breaker after the obstruction is cleared—the motor winding may be damaged.
- The check valve has seized and you are not comfortable replacing it.
- The discharge line needs re-routing to prevent recurring freezes.
- You suspect a failed capacitor or other internal motor component.
Any modification to the electrical circuit—new outlet, GFCI protection, hard-wiring—requires a licensed electrician.
Repair or replace?
A simple impeller clearing or check valve swap is a worthwhile repair on a pump that is otherwise in good condition. If the motor winding is damaged from running locked-rotor or dry, or if the pump is more than seven to ten years old, replacement is often the more reliable choice.
See our sump pump replacement cost guide for a breakdown of what the job typically involves, and use our Repair vs. Replace calculator to weigh the options.
How to prevent it
- Install an inlet screen or filter if your pit bottom has loose gravel that can enter the pump.
- Test the pump seasonally by pouring water into the pit and confirming clean start and stop cycles.
- Inspect the discharge line before each winter to ensure the exterior exit cannot freeze.
- Keep the float path clear—avoid storing items in or near the pit that can fall in and jam the float or impeller.
Estimated costs
| Item | Typical range (USD) | As of | Scope / source |
|---|---|---|---|
| Sump pump cleaning and impeller clearing (service call)† | $75–$200 | 2026 | United States · HomeFixHelper illustrative range — Verify with local quotes |
| Sump pump replacement (submersible, installed)† | $400–$900 | 2026 | United States · HomeFixHelper illustrative range — Verify with local quotes; see our sump pump replacement cost guide |
† Illustrative placeholder pending verified source data. Do not treat as a quote.
Costs vary by region, brand, and the specific failure. Always get written quotes from licensed local professionals.
Frequently asked questions
Will dry running damage my sump pump?
Yes. Most submersible sump pumps use the water in the pit for cooling. Running the pump without water—or with the pit nearly empty—quickly overheats the motor seal and bearings. If the float is stuck in the "on" position with no water present, cut power immediately and correct the float before running the pump again.
Can I clear a jammed impeller myself?
On many submersible pumps you can remove the pump from the pit, unscrew the bottom inlet cover, and remove debris by hand. Always unplug the pump completely first. If gravel or debris has broken the impeller vane itself, the pump needs professional service or replacement. Never put your fingers into the impeller housing with the pump plugged in.
How do I know if the discharge line is frozen?
Go outside and find where the discharge pipe exits the foundation. In freezing weather, hold your hand near the outlet while the pump is running—you should feel water flow. No flow while the pump hums strongly suggests a freeze. Pouring warm (not boiling) water over accessible sections of the pipe may clear a minor freeze; a persistently freezing line needs re-routing or insulation.
Is an airlock a common cause?
Airlocks are relatively uncommon in properly installed sump systems because the discharge pipe normally has a small weep hole drilled just above the pump to allow air to escape. If that weep hole is absent or plugged, an airlock can form and prevent the pump from priming. Check your pump's installation manual for the recommended weep-hole location.
Sources
- Moisture Control Guidance for Building Design, Construction and Maintenance — U.S. EPA (link). Checked October 15, 2026. Supports: Guidance on foundation water management and sump system function.
- Sump pump owner's manual (your model) — Manufacturer documentation. Checked October 15, 2026. Supports: Model-specific impeller access, weep-hole requirements, and float adjustment.