Turn off the circuit breaker and unplug power to the pump. Confirm that the cord is in good condition.
Close shutoff valve located in discharge piping (ideally it is installed above the check valve).
(SKIP THIS STEP IF YOU DO NOT HAVE A SHUTOFF VALVE - we’ll test the valve later) Remove the check valve and visually inspect it for damage. Make sure it fully opens and closes.
Disconnect the sump pump from the discharge pipe and remove it from the basin.
Make sure the vent hole in the discharge pipe is clear from debris.
Clean debris from the exterior of the pump (a garden hose may help a lot with this step).
Check the pump screen for any blockages or debris and clear any obstructions.
Reconnect the check valve and replace the sump pump back in the basin.
Restore power by plugging in the power cord and turning on the breaker.
Test the pump by dumping a bucket of water into the basin. It should turn on and empty the pit until the float switch turns it off.
(NO SHUTOFF VALVE ONLY) Inspect the check valve. A faulty check valve will allow water to flow back into the pit after the pump shuts off. Cycle the pump and watch the water level to see if it rises and listen for gurgling/water flowing backwards.
Check the alarm (if present) and pump float(s) to see if they are mounted properly and free from obstructions.
The cheapest insurance policy is to make sure you have a backup pump on hand.