How a sump system works
A sump pit sits at the lowest point of the basement floor. Drain tile around the foundation collects groundwater and carries it to the pit. When the water rises, a float switch turns on the pump, which pushes the water up a discharge pipe and out of the house, usually to the yard. A check valve on the discharge stops the water in the pipe from running back down when the pump shuts off.
Basements across South-Central Pennsylvania depend on these systems. NOAA’s 1991–2020 climate normals show roughly 41 to 46 inches of precipitation a year at stations across the region, and spring snowmelt adds to it. Pumps that sit idle all summer are often the ones that fail on the first big storm.
Water and electricity
If the basement is already flooding, don’t walk into standing water near the pump, outlets or the panel. Shut off power to the basement from a dry location first, or wait for help.
Pump doesn’t run
- No power. Check the breaker and whether a GFCI outlet has tripped. Many pumps plug into a GFCI outlet; press reset.
- Stuck float. The float can jam against the pit wall or the pump’s own cord. Make sure it moves freely.
- Failed switch. Float switches wear out, especially on pumps that cycle often.
- Burned-out motor. A pump that hums but doesn’t move water may have a seized impeller or failed motor.
You can test a pump by slowly pouring a bucket of water into the pit. It should start, empty the pit, and shut off.
Pump runs constantly or cycles too often
- Failed check valve. Water in the discharge pipe falls back into the pit and the pump keeps pumping the same water. You may hear a thud when it shuts off.
- Float set too low or stuck down.
- High groundwater. During wet seasons some pumps legitimately run very often; the question is whether it keeps up.
- Frozen or blocked discharge line. In winter, the outside end of the discharge can freeze or be buried in snow, so water has nowhere to go. A pump running against a blocked line can overheat.
- Undersized pump for the amount of water coming in.
Water still comes in with the pump working
Not every wet basement is a sump problem. Water from wall cracks, window wells, gutters dumping next to the foundation, or a sewer backup through a floor drain needs a different fix. If the water at the floor drain smells like sewage, the issue is the main line; see sewer line repair.
What a plumber checks and fixes
- Pump replacement with an appropriately sized unit. Submersible pumps are quieter and common in finished basements; pedestal pumps sit above the pit and are easier to service.
- Switch replacement, often with a more reliable vertical or electronic switch.
- Check valve replacement, installed so it can be serviced.
- Discharge line routing, including sloping it to drain and adding a freeze-resistant outlet.
- Pit lid to keep debris out and reduce humidity and radon entry; some radon systems use a sealed lid.
- Electrical: a dedicated circuit where needed.
Signs a pump is near the end
Sump pumps work hard in a short burst every wet season and sit idle the rest of the year, which is a tough life for a motor. Plan on replacement when you notice:
- Loud grinding, rattling or vibration while it runs.
- Running longer than it used to for the same amount of water.
- Rust on the housing or a discharge pipe that shakes violently.
- A switch that needs to be jiggled to start.
- Visible damage to the cord or plug.
Replacing a tired pump on a dry day costs far less than replacing it, plus drywall and carpet, during a storm.
Choosing a replacement pump
Things a plumber will weigh with you:
- Capacity: how many gallons per hour it moves at the height it has to lift the water. A pump that is too small can’t keep up; one that is far too large short-cycles.
- Housing: cast iron dissipates heat and lasts longer under heavy use; thermoplastic is lighter and less expensive.
- Switch type: vertical and electronic switches need less room in the pit and stick less often than tethered floats in small pits.
- Pit size: a small pit makes any pump cycle more; sometimes enlarging the pit is part of the fix.
- Noise: submersible pumps are quieter in finished basements.
Backup options
A sump pump is only as reliable as the power to it, and storms knock out power exactly when pumps are needed most.
- Battery backup pumps sit alongside the main pump and take over during outages or if the main pump fails.
- Water-powered backups use municipal water pressure to pump the pit without electricity, where the code and water utility allow them.
- High-water alarms sound when the pit rises above normal level, giving warning before the floor gets wet.
A plumber can recommend which fits your house and how long a battery system can be expected to run.
Simple maintenance
- Test the pump every few months and before spring with a bucket of water.
- Clear debris from the pit and the pump intake.
- Check that the discharge line outside is clear, not frozen and points away from the foundation.
- Make sure the float moves freely.
- Replace backup batteries on the manufacturer’s schedule.
Discharge rules
Many municipalities prohibit connecting sump pumps to the sanitary sewer, because the extra water overloads treatment plants and can cause sewer backups elsewhere. Some also regulate where discharge may go relative to property lines and sidewalks. If your pump discharges into a floor drain or laundry tub, ask a plumber whether it needs to be rerouted.
Sump pump questions
How often should a sump pump run?
It depends on the water table and the weather. Frequent running after heavy rain is normal; running every few minutes in dry weather suggests a check valve, float or groundwater problem.
My pump hums but doesn’t pump. What’s wrong?
Often a jammed impeller, a clogged intake, or a failing motor. Unplug it before checking the intake.
Do I need a battery backup?
If the basement is finished or holds anything valuable, a backup pump or at least a high-water alarm is worth considering. Power outages and pump failures tend to happen during the same storms.
Can my sump pump drain into the sewer?
In many municipalities, no. Sump discharge into the sanitary sewer is often prohibited; check your local rules.
Why does my sump pit smell?
A dry pit can let soil gases in, and stagnant water can smell. A sealed lid and occasional flushing help. A sewage smell points to a different problem.
Related: drain cleaning, emergency plumbing, burst and frozen pipes, leak detection, water heater repair, water line replacement, how calls work and the areas we cover.