Sump Pump Not Working? Causes, Symptoms & What to Do
If a sump pump is not working, start with the symptom before assuming the motor is dead.
A silent pump, a humming pump, a pump that runs without lowering the water, a pump that never shuts off, and a pump that short-cycles all point to different failure patterns.
Common causes include float or switch problems, blocked discharge piping, check-valve problems, air lock, power loss, impeller obstruction, excessive head, incorrect sizing, or mechanical failure.
Safety First if Water Is Rising
Do not enter standing water where electrical equipment may be energized. The CDC advises not to enter standing water to reach a main power switch. If electrical circuits or equipment are wet or near water and the shutoff cannot be reached from a dry location, use a qualified electrician or emergency professional.
Do not open electrical panels, bypass switches, repeatedly reset a breaker, disassemble an energized pump, or use electrical tools while standing in water.
CDC electrical-hazard guidance →
If the basin is close to overflowing or water is already spreading across the floor, use Emergency Sump Pump Service.
Sump Pump Not Working: Symptom Guide
| Symptom | Common possibilities | Best next step |
|---|---|---|
| Pump is silent while the basin rises | Power loss, float obstruction, failed switch, motor failure | Urgent diagnosis if water is rising |
| Pump hums but does not move water | Air lock, blocked discharge, impeller obstruction, excessive head, motor problem | Do not rely on the pump; diagnose promptly |
| Pump runs but basin level barely falls | Discharge restriction, stuck check valve, worn pump, insufficient capacity at operating head | Check pump performance and discharge system |
| Pump will not shut off | Float stuck on, control problem, heavy inflow, discharge problem | Diagnose float and system load |
| Pump starts every few seconds | Small usable basin volume, float setup, check-valve backflow, high inflow | Correct the cycling cause |
| Water falls back after shutdown | Missing, leaking, stuck-open, or ineffective check valve | Check valve / discharge diagnosis |
| Pump works but basement still floods | Sewer backup, seepage, surface water, poor collection, insufficient capacity | Identify the actual water source |
1. Pump Is Silent and Will Not Start
A silent sump pump may not be receiving power, the float or switch may not be calling for the pump, or the motor may have failed.
- Power outage
- Tripped protective device or interrupted circuit
- Float blocked by the basin wall, piping, or debris
- Failed float or switch
- Mechanical binding
- Motor failure
From a safe, dry location, note whether the float appears obviously trapped and whether the home has lost power. Do not reach into an energized basin or open electrical equipment to test the circuit.
If the basin continues rising while the pump stays silent, the system needs prompt diagnosis.
2. Pump Hums but Does Not Pump
Zoeller’s current product-support guidance identifies air lock as one cause of a sump pump humming without pumping. Manufacturer troubleshooting also points to impeller restriction and discharge-system problems.
- Air lock
- Blocked or frozen discharge line
- Obstructed impeller
- Check valve stuck or installed incorrectly
- Total head beyond the pump’s useful capability
- Mechanical or motor problem
A humming pump is not providing flood protection if the basin water level is not dropping.
Zoeller current troubleshooting guidance →
3. Pump Runs but Water Barely Moves
If the motor runs but the basin does not fall at a useful rate, the problem may be the discharge path, the pump’s hydraulic performance, or a mechanical restriction.
- Blocked or partially blocked discharge piping
- Frozen exterior discharge
- Check valve stuck closed or restricted
- Impeller obstruction
- Excessive total dynamic head
- Pump no longer delivering adequate flow
- Incoming groundwater exceeding pump capacity
If the pump sounds normal but water is not leaving the property correctly, use Sump Pump Discharge Line Service.
4. Pump Will Not Shut Off
A continuously running pump can mean the float is unable to return to its off position, groundwater inflow is unusually high, or the system cannot lower the basin enough to satisfy the control.
- Float caught on the basin wall or piping
- Failed switch or control
- Heavy groundwater inflow
- Discharge restriction
- Water falling back through the discharge line
- Pump capacity too low at the actual operating head
Continuous operation is a symptom, not a diagnosis. Do not assume a larger pump is the answer until the float, check valve, discharge route, and inflow are evaluated.
5. Pump Turns On and Off Every Few Seconds
This is short-cycling.
Manufacturer troubleshooting guidance identifies several possible causes:
- Small usable basin volume
- Improper or restricted float travel
- Check valve missing, stuck open, or leaking
- Water falling back into the basin
- High groundwater inflow
- Pump capacity poorly matched to basin volume
Replacing the pump without fixing the cycling cause can expose the replacement pump to the same operating pattern.
6. Water Falls Back Into the Pit
The sump-pump check valve limits discharge water from returning to the basin after shutdown.
Zoeller’s current support guidance notes that a check valve can reduce short-cycling. A missing, stuck-open, leaking, or ineffective valve can force the pump to handle the same water repeatedly.
For water returning after each cycle, use Check Valve Installation or Discharge Line Service.
7. Pump Works but the Basement Still Floods
A working sump pump only handles water that reaches the sump system.
Basement water can also come from:
- Floor drains or plumbing fixtures during sewer backup
- Wall-floor joints or foundation seepage
- Window wells
- Doors or exterior stairwells
- Surface runoff
- Perimeter drainage that does not deliver water to the basin
If water is backing up through a floor drain, toilet, shower, laundry fixture, or other plumbing opening, use Sewer Backup Prevention rather than assuming the sump pump needs to be larger.
8. Power Is Out
A standard electric primary sump pump cannot provide normal pumping without power.
If the basin continues filling during an outage, a properly designed backup system is the relevant protection—not a larger primary motor.
CDC flood-preparedness guidance specifically recommends sump pumps with backup power as part of home flood preparation.
Battery Backup Sump Pump Installation →
9. Pump Suddenly Sounds Different
A new grinding, rattling, buzzing, or vibration deserves attention, especially when it appears with weak flow or unreliable cycling.
A loud thump immediately after shutdown can be water hammer rather than a dead pump. Zoeller describes water hammer as the effect of flow reversal when the check valve closes.
Noise by itself does not identify the failed component. Combine the sound with the water behavior before deciding whether the issue is the pump, valve, piping, or another part of the system.
10. The Pump Is Older and Becoming Unreliable
Age changes the repair-versus-replacement decision, but it does not identify the cause by itself.
As one current manufacturer benchmark, Zoeller estimates approximately 7–10 years of service under normal conditions. A pump within or beyond that range deserves more replacement consideration when it is also weak, noisy, intermittent, corroded, or repeatedly failing.
What You Can Safely Observe
From a dry, safe location, useful observations include:
- Is the pump silent, humming, or running?
- Is the basin level rising, falling, or unchanged?
- Does the float appear obviously trapped by the basin wall or piping?
- Is a backup or high-water alarm active?
- Did the problem start during a power outage?
- Is the exterior discharge visibly blocked by ice, snow, or obvious debris?
- Does water rush back into the basin after shutdown?
- Is the basement water clear, or does it have a sewage odor?
- Did a floor drain or plumbing fixture back up?
- Has the pump recently started cycling much more often?
Do not remove the pump, open electrical components, drill anti-airlock holes, bypass switches, manually manipulate energized equipment, or enter standing water to troubleshoot.
Repair or Replace?
| Finding | More likely path |
|---|---|
| Float obstruction on an otherwise healthy system | Diagnosis / component repair |
| Failed check valve | Check-valve repair or replacement |
| Blocked or frozen discharge | Discharge correction |
| Motor failure | Often pump replacement |
| Older pump with declining output or repeated failures | Replacement deserves stronger consideration |
| Pump is wrong for required flow/head | Re-size the system and select the correct replacement |
Use Sump Pump Repair when the cause is still uncertain. Use Sump Pump Replacement when the pump itself is clearly no longer dependable or correctly sized.
Sump Pump Not Working FAQ
Why is my sump pump not turning on?
Possible causes include power loss, a float that cannot move, a failed switch, mechanical binding, or motor failure. If the basin is rising and the pump remains silent, arrange prompt diagnosis.
Why is my sump pump humming but not pumping?
Possible causes include air lock, discharge blockage, impeller restriction, a check-valve problem, excessive head, or motor trouble. A humming pump is not protecting the basement if the basin level is not falling.
Why does my sump pump keep running?
The float may be stuck, groundwater inflow may be high, the discharge may be restricted, water may be returning through the check valve, or the pump may not have enough flow at the operating head.
Why does my sump pump turn on every few seconds?
This is short-cycling. Possible causes include limited basin volume, restricted float travel, check-valve backflow, high inflow, or a pump poorly matched to the system.
Why is the pump running but the basin is still full?
The discharge may be blocked, the pump may be air-locked or obstructed, the check valve may be restricting flow, or the pump may not provide enough capacity at the actual operating head.
What should I do if the sump pump stops during a storm?
Stay out of standing water where electrical equipment may be energized. Note whether the pump is silent, humming, running, or whether the power is out, and request urgent service if the basin continues rising.
Need Diagnosis or Repair?
If the sump pump is not turning on, hums without pumping, runs continuously, short-cycles, or cannot keep up with rising water, diagnose the complete system before guessing at a replacement.