A sump pump only matters on the day it has to work — and that’s the worst time to discover it doesn’t. If yours won’t kick on, is running nonstop, or is making a racket, most causes are things you can check in a few minutes. Here’s how I troubleshoot one before calling it dead.
⚠️ If the basement is actively flooding
Deal with safety first: standing water plus electricity is dangerous. If water is near outlets or the panel, don’t wade in — cut power at the breaker if you can reach it safely, and call a pro. Once it’s safe, work through the checks below.
Diagnose by symptom
| What it’s doing | Most likely cause | First thing to check |
|---|---|---|
| Totally dead, no hum | No power, or the float switch is stuck | Outlet/breaker and GFCI; then the float |
| Hums but won’t pump | Stuck impeller or jammed float | Power off, clear debris from the bottom |
| Runs but no water moves | Stuck or missing check valve, or frozen/clogged discharge line | The check valve and discharge pipe |
| Runs constantly | Float stuck “on,” failed check valve letting water flow back, or undersized pump | Float position and check valve |
| Loud rattle or grinding | Debris in the impeller or a worn pump | Clear the pit; if it persists, replace |
Start with power and the float switch
Most “dead” sump pumps aren’t broken. Confirm it’s plugged in, the breaker isn’t tripped, and the GFIC outlet hasn’t popped (press reset). Sump pumps are often plugged into a “piggyback” plug — make sure both the pump and the float plug are seated.
Then look at the float switch, the part that senses water level and turns the pump on. It’s the number-one failure point. If it’s wedged against the pit wall, tangled, or waterlogged, the pump never gets the signal. Free it so it can rise and fall, and reposition the pump so the float has room to move.
Check the impeller and the check valve
If it hums but won’t move water, cut the power and look in the pit — gravel or debris sucked into the intake can jam the impeller. Clear it. If it runs but water comes right back, the check valve on the discharge pipe (the one that stops pumped water from draining back into the pit) is stuck open or missing. And outside, make sure the discharge line isn’t clogged or frozen, which backs everything up.
Test it the easy way
Pour a 5-gallon bucket of water into the pit slowly. A healthy pump kicks on as the float rises and shuts off once the pit’s drained. If it does, you’re good. If it doesn’t, you’ve narrowed it to the float or the pump itself.
When to replace — and why a backup matters
Sump pumps last about 7–10 years. If yours is in that range and failing, replace it rather than nurse it — see my best sump pump picks. The bigger lesson from every flooded basement I’ve seen: a sump pump fails most often during the storm that knocks the power out. A battery backup sump pump is cheap insurance against exactly that. And if water has already gotten in, my guide on water-damage and burst-pipe repair costs gives a sense of what’s at stake.
Frequently asked questions
Why is my sump pump not turning on? Usually it’s power (a tripped breaker or GFCI) or a stuck float switch that can’t rise to trigger the pump. Check the outlet and free the float before assuming the motor is dead.
Why does my sump pump run but not pump water? The impeller may be jammed with debris, or the check valve on the discharge line is stuck open and letting water flow back in. The discharge pipe could also be clogged or frozen.
Why does my sump pump keep running constantly? A float stuck in the “on” position, a failed check valve letting water cycle back into the pit, or a pump too small for the water volume. Check the float and check valve first.
How long do sump pumps last? About 7 to 10 years. If yours is in that range and acting up, replace it, and add a battery backup so a power outage during a storm doesn’t leave you unprotected.
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