Sump pump not working? Troubleshooting by symptom
Short answer
If your sump pump isn’t working, start with the simple things: power, the breaker or GFCI outlet, the plug, the float switch and the water level in the pit. If it won’t stop, cycles on and off or makes noise, the float switch, the check valve or the discharge line is usually involved. Water and electricity don’t mix, so unplug the pump before you touch anything in the pit.
On this page
Safety first
I wouldn’t put my hands in the pit while the pump is plugged in. If you need to touch the pump or the float, disconnect the power first. Before you start, make sure the floor around the pit is dry and safe to stand on.
In Virginia, the 2021 residential code (E3902.5) requires GFCI protection for every 125- to 250-volt receptacle in a basement, and it makes no exception for the sump pump. If the GFCI trips again and again, call an electrician rather than plugging the pump into another outlet.
Sump pump not working: what to check first
| Symptom | What I check |
|---|---|
| Won’t start | First power, the breaker or GFCI, the plug, the float and the water level. Then a seized impeller or a failed motor. |
| Won’t stop | A float stuck in the up position, an undersized pump, more water coming in than the pump can handle, a partly blocked discharge, or a pump that runs but never gets the level down to its shutoff point. |
| Turns on and off constantly | A bad or missing check valve, a pit that’s too small, a float with very short travel, discharge water flowing back toward the foundation, a lot of inflow. |
| Noise or vibration | Debris, the impeller, a loose pipe, a check valve slamming shut, a worn pump. |
| Bad smell | A dirty pit, standing water or organic material; if it smells like sewer gas, the plumbing. |
| Frozen discharge | The frozen section of the line, and why it holds water. |
A normal groundwater sump shouldn’t clearly smell like sewage. I clean the pit first and look for standing water or organic material. If it smells like sewer gas, I check the plumbing before assuming it’s just the sump. For other basement odors, see Basement smells.
If the discharge line freezes, you don’t want the pump to keep pushing against a blocked pipe. Fix the frozen section first, and find out why the line is holding water.
The sump pump float switch
The float switch can fail in several ways: it catches on the side of the pit, the cord tangles, debris gets in the way, it sticks up or down, or the switch itself fails. With the pump unplugged, check that the float can move freely. To test it, I pour clean water into the pit and watch from outside the pit:
- the float rises;
- the pump starts;
- the level drops;
- the pump shuts off.
The sump pump check valve
The check valve keeps the water in the vertical discharge pipe from falling back into the pit when the pump shuts off. When it’s missing or fails, you may hear the pump turn on, turn off, the water drop back, and the pump turn on again.
Common check valve problems I see:
- the valve is stuck;
- debris;
- it’s installed backward;
- it’s the wrong size;
- it’s installed in an orientation that model doesn’t allow;
- a connection that makes it slam hard;
- a valve nobody can reach to replace.
I also see installations with no removable union, so replacing a small part means cutting pipe. Some pumps also need a small anti-airlock or weep hole in a specific spot. I follow the pump’s instructions for that, not a universal rule.
How often should a sump pump run?
There’s no normal number. One house can go weeks without the pump starting; another can run every few minutes during a storm and be working exactly as it should. What matters more is what happens to the water level. If the pump starts and clearly lowers the pit, it’s moving water. If it runs nonstop and the level keeps rising, there’s a problem. If it cycles every minute or two for long periods, I would look into it. That interval is my field criterion, not a standard.
What I want to rule out:
- a failed check valve;
- discharge water recirculating back to the pit;
- a small pit;
- an undersized pump;
- unusually high groundwater.
How to test a sump pump
- Make sure the floor around the pit is dry and safe to work on.
- Look over the cord, the plug, the pit and the discharge.
- Disconnect the power if you’re going to move anything inside the pit.
- Check that the float moves freely.
- Plug the pump back in.
- Slowly pour clean water into the pit.
- Wait for the float to turn the pump on.
- Check that the water level drops.
- Check that the pump shuts off on its own.
- Go outside and confirm that water is actually coming out of the discharge.
- When the pump stops, see how much water flows back into the pit.
- Test the backup and the alarm separately.
I would do this three or four times a year, and before stormy periods. That schedule is my maintenance recommendation, not a code requirement. For backup pumps and alarms, see Sump pump battery backup and alarms.
Repair or replace, and who to call
| Usually a repair | Time to think about replacing the pump |
|---|---|
| Check valve | The motor fails |
| A simple float | The impeller is badly damaged |
| Discharge line | It trips the breaker repeatedly |
| A blockage | It’s badly corroded |
| A fitting | It has already failed several times |
| It’s old and the whole basement depends on it |
- Plumber: the pump, piping, valves and many backup installations.
- Electrician: the outlet, circuit, breaker, GFCI or any electrical problem.
- Waterproofing or drainage contractor: when the problem is in the pit, the perimeter drain or the design of the whole drainage system.
I wouldn’t let someone who only swaps pumps automatically diagnose a groundwater problem.
Sources
- International Code Council, 2021 Virginia Residential Code, Chapter 39, section E3902.5. Checked October 17, 2026.