Start at the pit, not the box. Before a new pump comes off the truck, look at what the old one has been doing. A pump that runs often, runs long, or leaves silt in the bottom of the pit is telling you what the replacement has to handle. Write down the pit diameter and depth, the discharge pipe size, whether a check valve is already in the line, and where the discharge exits the house.
Before the Old Pump Comes Out
Turn off the power at the breaker and mark that breaker so no one restores it while your hands are in the pit. If the pump is hardwired rather than plugged in, the wiring work belongs to a licensed electrician. Check the new pump's inlet and outlet sizes against the pipe you already have. A mismatch means fittings, and fittings are where leaks start.
Pulling the Old Pump
Loosen the discharge union first, then lift the pump out by its handle. Do not lift it by the cord. Note how the float sits and which way the check valve faces, because the new pump has to match that layout. Scrape out silt and gravel, and look at the pit liner for cracks or a loose lid seal.
Setting the New Pump
Place the pump on the base of the pit, clear of the walls, so the float can swing without touching anything. Fit the check valve on the discharge side with its arrow pointing toward the outlet. Use a union so the next replacement does not require cutting pipe. Secure the discharge pipe so it does not shift when the pump kicks on. The outlet should carry water away from the foundation, not back toward it.
Power and Backup
Connect the pump through the correct plug, or have the electrician hardwire it as specified. If you have a battery backup unit, it is a separate pump with its own float and battery. Look at the battery label and the install record for it, because the backup has its own service clock.
The Test Run
Lift the float by hand, or pour water into the pit slowly. Watch the pump start, watch water move through the discharge, and watch it stop when the level drops. Listen for chatter from the check valve, and look for water running back into the pit after the pump shuts off. A clean shutoff with no backflow means the check valve is seated.
Record the Job
Write the install year on the pump body or in the file, keep the receipt and the wiring note together, and record the discharge route. That install year is your planning starting point. The published service life figures are in the tables on this site.