Sump Pump Not Working? What to Check, Step by Step
A sump pump only gets noticed when it stops doing its job. That can mean water on the basement floor, a pit that keeps filling, or a motor that will not shut off in the middle of the night. The good news is that a sump pump is a simple system. Power reaches the pump, a float tells it when to run, the pump pushes water up a pipe, and a valve keeps that water from coming back. When something goes wrong, it is one of those parts.
This guide walks through eight checks you can do yourself, in the order they are worth doing, and explains what each result may mean. None of them ask you to open the pump or touch any wiring.
Quick symptom guide
Start with the row that matches what you are seeing. The causes are possibilities, not a diagnosis.
| What you notice | Check first | Possible causes |
|---|---|---|
| Pit filling, pump silent | Power, then the float | Tripped breaker or outlet, stuck float, failed switch or motor |
| Pump runs, water level stays high | The pipe outside | Blocked or frozen discharge line, clogged intake, damaged impeller |
| On and off every few seconds | Listen when it stops | Failed check valve, float with a very short range |
| Runs nonstop, pit nearly empty | The float | Float stuck on, failed switch |
| Grinding, rattling or humming | Unplug, then look | Debris in the intake, jammed impeller, worn motor |
| Water pooling at the foundation outside | The end of the pipe | Discharge emptying too close to the house |
Check 1: Is it getting power?
A pump with no power looks exactly like a dead pump, so rule this out first. Check that the plug is fully in the outlet. If the outlet has test and reset buttons, see whether it has tripped. Then look at your breaker panel for a breaker that has moved to the off or middle position.
If you reset an outlet or breaker and it trips again, leave it off. Repeated tripping can point to a problem with the pump, the cord or the circuit, and that is a job for a professional.
Check 2: Can the float move?
The float switch is what tells the pump to start. As water fills the pit, the float rises, and at a set height it switches the pump on. As the pump empties the pit, the float drops and switches it off. Some floats hang on a short cord (a tethered float). Others slide up and down a vertical rod between two stops.
A vertical float switch: the float rides up with the water, hits the upper stop and starts the pump, then drops back to the lower stop and shuts it off.
With the pump unplugged, look into the pit. A float can get caught on the pit wall, on the discharge pipe or on the pump's own power cord, or it can be held down by debris. If it cannot rise, the pump never gets the signal to run. If it is stuck high, the pump may never get the signal to stop. Plug the pump back in once you have looked.
Check 3: Is the pit full of debris?
Gravel, silt, leaves and small objects can collect at the bottom of the pit over time. They can block the pump's intake, jam the float, or get drawn into the pump. If the bottom of the pit is buried in sediment, that alone can explain weak pumping or new noises. Cleaning a pit means working around the pump and its power, so if you are not comfortable doing that safely, ask a plumber.
Check 4: It runs, but the water stays
If you can hear the motor and the water level is not dropping, the water is either not getting into the pump or not getting out of the house. Go outside while the pump runs and look at the end of the discharge pipe:
- Nothing coming out: the line may be blocked, frozen or disconnected somewhere along its route.
- A weak trickle: the intake may be clogged, or the impeller inside the pump may be damaged.
- Water coming out of a joint or crack: the pipe may have come apart.
In a Lancaster winter, an outdoor discharge line can freeze, especially at the end where water sits. Look for ice at the outlet.
Check 5: It turns on and off every few seconds
Short, rapid cycles can be hard on a pump. One possible cause is the check valve, a one-way valve on the discharge pipe. When the pump stops, the water already in the pipe should stay there. If the valve has failed, that water falls back into the pit, the float rises again, and the pump restarts to move the same water.
Left: a working check valve closes when the pump stops and holds the water in the pipe. Right: a failed valve stays open and the water drops back into the pit.
To check, stand near the pit when the pump shuts off and listen. A rush of water running back down the pipe points to the valve. A float switch set with a very short range between on and off, or a pit that is small for the amount of water coming in, can also cause short cycles.
Check 6: It runs and will not stop
A pump that runs nonstop during a heavy storm may simply be keeping up with the water. Look into the pit. If the water is high and the pump is running, it is doing its job. If the pit is nearly empty and the motor keeps going, the float may be stuck in the on position or the switch may have failed. Running with no water can damage some pumps, so if the pit is dry and the pump will not stop, unplugging it until someone looks at it may protect it.
Check 7: New noises
Grinding, rattling or a loud hum can come from debris in the pump, a jammed or damaged impeller, worn parts or a motor that is struggling. A single thud in the pipe each time the pump stops can be the check valve closing, which is different from a failure. Unplug the pump before you look, and if the noise is coming from inside the pump, leave it to a plumber.
Check 8: Where is the water going?
Follow the discharge line outside. The water should leave the pipe and flow away from the house. If the outlet is buried in leaves, soil or snow, or if it empties right next to the foundation, the same water can soak back down and return to the pit, which keeps the pump working harder than it needs to.
If you are thinking about changing where your pump discharges, check with your municipality first. Some Pennsylvania municipalities bar connecting a sump pump to the sanitary sewer.
How to test the pump
Your pump's manual may describe a test. One way is to pour water slowly into the pit from a bucket until the float rises and the pump starts. Watch that it empties the pit, that water comes out of the pipe outside, and that it shuts off on its own when the level drops. Keep your hands out of the pit while you do this. Testing before the wet season can show a problem while there is still time to fix it.
When to stop and call
- The pit is filling and the pump will not start.
- Water is on the basement floor.
- A breaker or outlet trips again after you reset it.
- You smell burning, or the pump or cord is very hot.
- The noise is coming from inside the pump.
- You cannot check something without standing in water.
When you call, it helps to describe which checks you did and what you saw. If you are hiring someone in Pennsylvania, you can ask for their home improvement contractor registration number. Under the state's Home Improvement Consumer Protection Act, contractors who do $5,000 or more of home improvements a year must register with the Office of Attorney General, and work priced over $500 needs a written contract. You can check a registration at attorneygeneral.gov or by calling 1-888-520-6680.
Questions
How do I reset my sump pump?
Sump pumps do not have a standard reset button. If the pump plugs into an outlet that has test and reset buttons, that outlet may have tripped and can be reset. If a breaker has tripped, it can be switched back on at the panel. If either one trips again, leave it off and call, because something may be wrong with the pump or the wiring.
Why is my sump pump running when it is not raining?
Water can keep reaching the pit after the rain stops, for example as snow melts or the ground drains. If the pit is nearly empty and the motor still runs, the float may be stuck in the on position or the switch may have failed.
Can I pour water in the pit to test my sump pump?
One way to test is to pour water slowly into the pit until the float rises and the pump starts, then watch it shut off as the level drops. Check your pump's manual first, and keep your hands out of the pit while the pump is plugged in.
Is it safe to unplug a sump pump?
Unplugging it stops it from removing water, so only do it when there is a reason, such as the pump running dry, smelling of burning or being very hot. Do not unplug anything while you are standing in water.
Sources: Pennsylvania Office of Attorney General, Home Improvement Scams brochure (HICPA)
This guide is general information, not advice for your specific home. Lancaster Sump Pump Help is a referral line that connects callers with independent local plumbers.