1. Clean the screen
Unplug the sump pump, disconnect it from the discharge pipe, and pull the pump out of the sump. Hose away any debris on the screen at the pump’s base and rinse off its housing. Lubricate the pump bearings, if required. (Consult the owner’s manual if you’re unsure.)
2. Inspect the check valve
If its internal flap doesn’t swing freely, flush it out, and if you see mineral deposits, soak it in vinegar. Make sure its arrow points up when reconnecting it to the discharge pipe.
3. Test the float switch
Pour a few gallons of water into the sump. If it comes on and sucks out the water, the switch (and pump) are good to go. If not, repair or replace the switch.
4. Exercise the outlet
Per code, a sump pump has to be plugged into a GFCI receptacle. For your safety, press its test and reset buttons.
5. Got a backup battery?
Top up its cells with distilled water, as needed.