How to Replace a Sump Pump
Updated February 20, 2026
Remove a failed sump pump and install a new one. Covers sizing, pit prep, discharge connections, and float switch setup. Prevent basement flooding before it happens.
Overview
Sump pumps last 7-10 years on average. When they fail, you find out during the worst possible moment -- a heavy rain with water rising in the pit. Replacing a sump pump before it fails completely is smart maintenance. The job takes 1-2 hours: disconnect the old pump, clean the pit, lower the new one in, connect the discharge, set the float, and test. Match or exceed the old pump's capacity (GPH at your head pressure). This is also the time to add a battery backup if you do not have one.
What You'll Need
Safety First
- Unplug the old pump before reaching into the pit. Even with the float in the off position, a surge or float activation could start the pump while your hands are near the impeller.
- Sump pits can accumulate methane or sewer gas in rare cases. If you smell gas when you open the pit, ventilate the area before working.
Step-by-Step Instructions
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Choose the Right Replacement Pump
Check the old pump's nameplate for GPH (gallons per hour) rating, HP (horsepower), and voltage. Match or exceed these specs. Measure the vertical distance from the pit bottom to where the discharge exits the house (this is the head pressure). A pump rated at 3,000 GPH at 0 feet may only deliver 1,500 GPH at 10 feet of head. Submersible pumps are standard for most residential pits. Pedestal pumps are for narrow pits where a submersible will not fit.
Tip: If the old pump struggled during heavy rain (ran constantly or could not keep up), size up. Going from 1/3 HP to 1/2 HP is a common and worthwhile upgrade. Cast iron pumps are quieter and last longer than thermoplastic. -
Unplug and Remove the Old Pump
Unplug the pump from the outlet. If it uses a piggyback plug (two-plug system), unplug both. Remove the pit cover. Disconnect the discharge pipe from the pump -- this is usually a rubber coupling with hose clamps or a threaded connection. Lift the old pump straight up and out of the pit. It will be heavy with water. Let it drain over the pit.
Tip: Note how the discharge pipe connects and the pipe size (usually 1-1/2 inch). Take a photo. You will replicate this connection on the new pump. -
Clean the Pit
With the pump out, clean the pit. Remove gravel, mud, debris, and any solid material that has accumulated. Check that the pit liner is intact (if there is one). Ensure the pit bottom is flat and level so the new pump sits stable. If there is standing water, bail or shop-vac it out so you can see the bottom.
Tip: A layer of clean gravel (1-2 inches) on the pit bottom helps prevent mud and debris from clogging the new pump's intake screen. Use washed pea gravel. -
Install the New Pump
Attach the discharge adapter to the new pump per the manufacturer's instructions. Most pumps include a check valve -- install it on the discharge pipe above the pump to prevent backflow. Lower the pump into the pit centered and level. Connect the discharge pipe using the same method as the old pump (rubber coupling, threaded, or glued PVC). Make sure the float switch has clearance to move freely without catching on the pit wall, discharge pipe, or power cord.
Tip: If the old system had no check valve, add one now. Without a check valve, water in the discharge pipe flows back into the pit when the pump shuts off, causing the pump to cycle unnecessarily and shortening its life. -
Set the Float Switch
The float switch tells the pump when to turn on and off. Tethered floats: adjust the tether length so the pump activates when water is 3-4 inches above the pump intake and shuts off when water drops to 1-2 inches above intake. Vertical floats: adjust the rod position. Pour water into the pit slowly and watch the float activate. The pump should turn on well before water reaches the top of the pit and shut off cleanly without short-cycling.
Tip: Short-cycling (pump turns on and off rapidly) means the float range is too narrow. Lengthen the tether or widen the activation gap. Short-cycling burns out motors fast. -
Test with Water
Plug the pump in. Pour 5 gallons of water into the pit and watch a complete cycle. Pump should activate, remove the water, and shut off cleanly. Check the discharge pipe exit outside -- water should flow freely. Check all connections for leaks. Replace the pit cover. Run the test two more times to confirm consistent operation.
Tip: After testing, mark the date of installation on the pump or pit cover with a permanent marker. Sump pumps should be replaced proactively every 7-10 years. Knowing when it was installed makes planning easier.
Pro Tips
- Install a battery backup sump pump at the same time. Primary pump fails or power goes out during a storm -- the backup activates automatically. $150-300 for the backup unit, potentially saves thousands in flood damage.
- Install a sump pump alarm ($15-25) that sounds when water rises above the normal activation point. Early warning if the pump fails.
- Test the sump pump every 3-4 months by pouring water into the pit. Do not wait for the next rain to find out it is dead.
- If the discharge line exits at ground level and freezes in winter, install a freeze-relief fitting near the foundation wall. Opens automatically if the main line freezes.
- Keep the pit cover in place at all times. Prevents debris from falling in and reduces the risk of radon entry and moisture evaporation into the basement.
When to Call a Pro
Call a plumber if the discharge pipe needs rerouting or is buried and inaccessible, if you want a battery backup system with automatic switchover, if the pit needs to be enlarged or a new pit installed, if you need a sewage ejector pump (handles solids -- different from a standard sump pump), or if you want professional sizing based on your water table and pit inflow rate.