A sump pump that is not turning on usually has no power, a stuck float, or a failed switch or motor. Check the breaker and GFCI outlet first, then make sure the float can move freely and the pit has enough water to lift it. Unplug the pump before you touch anything in the pit.
Is the pump getting power?
Start at the outlet, not the pump. Liberty Pumps, a maker of sump and sewage pumps, lists the first possible causes of a pump that does not start as a "tripped circuit breaker, tripped GFCI, blown fuse, or other interruption of power." Its fix is to reset the breaker or GFCI, replace a blown fuse with a properly sized one, and check that the unit is securely plugged in.
A GFCI outlet is the usual suspect in a damp utility area. Wayne's manual says it directly: "In damp areas, GFCI breakers may trip, effectively shutting off the sump pump." Press the reset button, and if the pump comes on, you have your answer. If the GFCI trips again as soon as the pump runs, Wayne's troubleshooting chart lists a bad GFCI or a bad pump as the causes, and it says to have an electrician replace the GFCI or replace the pump. A pump that trips a GFCI over and over is telling you something, so don't just keep resetting it. Our page on why a sump pump keeps tripping the GFCI walks through how to tell which one it is.
Two other power problems show up on Liberty's chart. One is low line voltage: it says to check the voltage, and if it is under 108 V, to check the wiring size. The other is an extension cord. Liberty says not to use one to power the pump, and the manual explains that extension cords can overload both the product and the cord's supply wires. A sump pump belongs on its own properly wired outlet.
Wiring and voltage checks are electrician work. Liberty's manual says installation and maintenance of pumps, controls and wiring should be done by qualified personnel.
Can the float move freely?
If the outlet has power and the pump still sits there, look at the float. The float is the part that rises with the water and tells the pump to start. It is the most common mechanical reason a pump fails to run.
Liberty lists two causes tied to the float. First, the float switch may be unable to move to the "on" position because of interference in the basin or another obstruction. Its fix is to position the pump or float switch so it has clearance to move freely. Second, the float switch may simply be defective, and the fix is to replace it.
Wayne points to a cause that people miss. It says to make sure the pump is standing upright, because "vibrations during operation can cause it to fall or tilt onto one side. This can jam the float so it can't activate the pump." A pump that tilted against the pit wall can look fine and still never start.
Check for debris too. Wayne says to inspect the pump three to four times a year "for pump movement or buildup of debris on the switch or float," to reposition the pump if it has moved, and to remove any debris that could interfere with the switch.
Do the safe check first. Zoeller, another pump maker, says common troubleshooting steps include checking the power source, making sure the pump is plugged in correctly, inspecting the float switch and clearing any clogs or blockages. Before you reach into the pit, unplug the pump. Liberty's manual says to "always disconnect pump(s) from power source(s) before handling or making any adjustments." If you need to lift the float by hand to test it, it also warns: "Do not use metal or any other electrical conducting material to raise the float or contact anything inside an electrically live sump pit." Lifting a float with the pump plugged in is a shock risk. If you are not sure the power is off, stop and call a plumber or electrician.
A simpler and safer way to test the float is to add water. Pour a bucket into the pit. If the float rises and the pump starts, the float works and the pit was just too dry to trigger it. Liberty lists "insufficient liquid level" as a cause, so it is worth checking that the water is allowed to rise high enough to activate the float.
Is the pump jammed or worn out?
If power is fine and the float moves but the pump still won't run, the pump itself is the likely problem.
Liberty's chart lists these remaining causes for a pump that does not start: an obstructed impeller or volute, loose wiring connections, and a defective motor. Wayne's chart lists the motor, the switch, a clogged inlet screen, and switch obstruction. Wayne's remedies are to replace the pump, replace the tether switch or the pump, remove the debris, and clear the obstruction.
A clogged inlet is worth a look. Liberty says that if the pump becomes clogged, the inlet screen can be removed to reach the impeller, and once the obstruction is removed, the anti-airlock hole should be cleaned. That means unplugging the pump and taking it out of the pit, which is more than most people want to do in a wet basement.
Age is a factor too. Wayne's manual for its tether-float pumps says: "Replace the tether switch every two (2) years." It calls this maintenance required to lower the risk of improper pump operation, switch failure and flooding. A pump that has never had its switch replaced may fail to start simply because the switch is worn.
When the motor is the problem, Wayne's chart says to replace the pump. Liberty says disassembly outside an authorized repair facility voids its warranty, so don't open the motor housing yourself.
What if the pump runs or hums but does not pump water?
A pump that turns on but does not move water is a different problem from one that will not start, so treat it separately.
Liberty lists these causes for a pump that runs or hums but does not pump: a blocked or restricted discharge line, a check valve stuck closed or installed backward, a closed gate or ball valve, total head beyond the pump's capability, an obstructed impeller or clogged inlet screen, and an airlocked pump. For an airlock, its fix is to turn the pump off, let it sit for several minutes, and restart it, then clear the anti-airlock hole.
Airlock happens when air is trapped around the impeller and cannot escape. Liberty explains that the impeller then spins in an air pocket and cannot prime. That is why many pumps have a small vent hole, and why Liberty says a small spray of water from it is normal while the pump is running.
Any of these can happen in the middle of a storm, when you need the pump most. If you cannot get it running, do not wade into a flooded basement to work on a live pump. Turn off power at the breaker only if you can reach the panel without standing in water, and call a plumber.
### What should you do next?
If the pump is dead and water is rising, the first job is to protect the room, not the pump. Move valuables up and keep power away from standing water. Then get the pump running again, or replaced. If you have a battery backup, our guide on whether you need a battery backup for a sump pump explains how it can carry you through.
Once it works again, find out why it failed so it does not fail again. Our guide on how to maintain and test a sump pump covers the monthly and quarterly checks. If the pump runs when it should not, see why a sump pump runs constantly. A sewage ejector pump is a different machine with its own failure list; see why a sewage ejector pump runs but does not pump and why a sewage ejector pump keeps tripping the breaker.
If the pump is dead and you would rather not work around a wet pit, HQ Plumbing and Air can diagnose it or replace it. We answer 24/7, we are licensed and insured, and you hear the price before work starts.