Troubleshoot a sump pump by checking power first, then the float switch — the most common fail point — then the inlet screen and discharge line.
For the full breakdown, see our best Battery Operated Sump Pump guide.
Most breakdowns trace back to four inspectable parts: the power supply, the float switch, the inlet screen, and the discharge line. Test those parts one at a time, in that order, until the fault shows itself. Never work on a live pump: turn off the breaker, then unplug the cord, before touching anything.
Start With Power, Then the Float Switch
A silent pump is usually starved of electricity or riding on a dead float switch. Confirm the outlet is live by plugging a lamp into it, then check the breaker panel and any GFCI outlet. If the GFCI tripped, reset it and try again.
Pentair’s sump pump troubleshooting guide calls the float switch the most common fail point, and its bypass test takes seconds. Unplug the float switch’s plug from the pump cord, then plug the pump straight into the wall for just a moment — a dry pump can overheat.
Runs But Won’t Empty the Pit? Clear the Intake Path
A pump that runs while water barely drops usually has a flow problem, not a motor problem. The culprits: a clogged inlet screen, debris jammed against the impeller, an obstructed discharge line, or a check valve that sticks closed.
- Inlet screen. Grit and debris accumulate over a season and choke the intake.
- Impeller. A pebble or twig can wedge between blades and stall flow while the motor spins.
- Discharge line. A kink, closed valve, or winter freeze blocks outflow. Disconnect the pipe and confirm water moves freely before servicing anything else.
- Check valve. Stuck shut, it lets nothing leave the pit; stuck open, it lets water drain back. Both look like bigger problems than they are.
If the line is clear, service the pump itself. FEMA’s sump pump maintenance guidance supports this order:
- Turn off the breaker and unplug the power cord.
- Lift the pump out of the pit and remove the check valve.
- Rinse debris from the exterior with a garden hose and scrub the inlet screen with a wire brush.
- Clear the impeller from underneath if your model allows access. Some pumps require removing the bottom plate—check the owner’s manual first.
- Reinstall the check valve, reconnect the pump, and restore power.
Pour a bucket of water into the pit. The float should rise, the pump should switch on, and the pit should empty—that confirms the repair.
Short-Cycling, Noise, and Keeping It Fixed
A pump that runs constantly or bursts on and off usually has a float switch stuck raised, or a check valve that won’t seat and lets water flow back into the pit. Free the float if debris caught it; replace a faulty check valve. Grinding or vibrating pumps usually contain gravel or sand, or have worn internal parts worth a professional’s look.
| Symptom | Likely Cause | Working Fix |
|---|---|---|
| Pump will not turn on | Tripped GFCI or breaker, dead outlet, failed float switch | Restore power, verify the outlet, run the float bypass test |
| Runs but will not drain | Clogged inlet screen or impeller, blocked discharge line | Clear the line, scrub the screen, remove debris from the impeller |
| Runs constantly | Stuck float switch, check valve not seating | Free the float, replace the check valve |
| Short-cycles | Float switch set too low or caught on debris | Clean the pit floor and reset the float position |
| Noisy or grinding | Debris inside the pump or worn bearings | Clean the pump; have worn parts serviced |
Keep the pump on an annual calendar. Assess the whole setup once a year, and test a battery backup two to five times a year, depending on model and installation. Call a professional when the pump trips the breaker repeatedly, runs hot, or still fails after these checks—repeated electrical faults are a sign to stop testing.
If failures line up with storms and power outages, household current disappears right when needed most.
FAQs
Why does my sump pump keep running after the pit is empty?
A float switch stuck raised tells the pump the pit is full when it is not, so the pump never shuts off. A check valve that fails to seat causes the same symptom by letting water drain back, restarting the cycle. Free debris around the float first; if the check valve is worn, replace it.
How do I test a sump pump float switch?
Unplug the float switch’s plug from the pump cord and plug the pump directly into a wall outlet for one or two seconds. If the motor runs, the float switch is bad. If the motor stays silent, the problem is upstream—the outlet, wiring, or motor—and a professional should take over.
How often should a sump pump be serviced?
Assess the pump at least once a year, and clean the inlet screen more often if the pit collects debris. Also inspect the pump after heavy storms, since that is when failures surface.
References & Sources
- Pentair. “Sump Pump Troubleshooting.” Covers power, float switch, clogging, and discharge and check-valve checks.
- FEMA. “Sump Pump Maintenance.” Provides the safe service order, inlet screen cleaning guidance, and the bucket test.
