What is a Sump Pump?

A sump pump is an automatic electrical pump installed below a basement or crawlspace floor that removes groundwater before it reaches the living space.

The Two Things Most Homeowners Get Wrong

The pump itself is reliable hardware. Most basement water problems trace back to two oversights: leaving the sump pit open and never testing the pump until it fails during a storm. An open pit pulls radon and moist air into the house through the stack effect. An untested pump discovers its own failure exactly when the pressure is highest, during a heavy rain that may have already cut the power.

Where You’ll Find It

Sump pumps are common in:

• Basements, particularly in homes with high water tables, clay-heavy soil, or lots in low-lying areas
• Crawlspaces, where groundwater or surface runoff collects beneath the floor joists
• Homes with finished lower levels, where even minor flooding causes significant damage

If your home sits on a slope, in a valley, or in a region with heavy seasonal rain, there’s a reasonable chance it has one, or should.

How the System Works

The pump doesn’t operate alone. It’s the last stop in a drainage chain that begins at the foundation perimeter.

Most installations include a network of perforated drain pipes running along the base of the foundation walls, sloped to carry water toward a central collection point. That point is the sump pit: a hole cut into the lowest spot of the foundation slab, typically 18–24 inches in diameter and 2 feet deep. As groundwater rises or surface runoff accumulates, it drains into the pit rather than seeping through the walls or floor.

When water in the pit reaches a set level, a float switch triggers the pump. The pump draws water through an inlet screen at its base and expels it through a discharge pipe that exits the house. That pipe must terminate at least 20 feet from the foundation, far enough that the discharged water doesn’t simply cycle back through the soil and into the pit again.

The two main pump types differ in where they sit:

• Pedestal pumps mount above the waterline, with only the intake extending into the pit. They cost roughly $60–$200 and are easier to inspect and service. The motor runs exposed to air, which means they’re louder.
• Submersible pumps rest fully underwater inside the pit, with sealed, oil-cooled motors. They run quieter and typically cost up to $600. Because they’re submerged, servicing requires pulling the unit out of the pit.

Neither type is universally better. Submersible units suit finished basements where noise is a concern; pedestal units make sense where easy access matters more than acoustics.

The Open Pit Problem (and Radon)

Most homeowners treat the sump pit as a minor detail. It isn’t.

A home’s stack effect (the tendency of warm air to rise and escape through upper floors and the roof) creates negative air pressure in the basement. That low pressure pulls air in from every available gap: wall cracks, floor joints, and any unsealed opening. An uncovered sump pit is a direct channel from the soil beneath your foundation into your home’s air supply.

Soil gas carries moisture and, in many areas, radon. The EPA identifies cracks and openings in the foundation as the primary pathway for soil gas and radon entry into a home, and an uncovered sump pit is, structurally, exactly that: a hole cut straight through the slab into the soil below. Radon is the second-leading cause of lung cancer in the United States, and it’s odorless and invisible, so you won’t notice it without a test.

The fix is an airtight, childproof cover. This is a code requirement, not a suggestion. For homes with a radon mitigation system, the cover can be fitted with a gasketed opening for the vent pipe, letting the sump pit serve as the suction point for active sub-slab depressurization. If your pit has no cover, or a loose plastic sheet that isn’t sealed, that’s worth addressing now.

Common Problems

Problem	What It Means	What You’d Notice
Float switch stuck or fouled	Pump doesn’t activate when water rises	Water in the pit with no pump response
Inlet screen clogged	Reduced flow; motor strain	Pump runs but water level stays high
Discharge pipe frozen or blocked	Water has nowhere to go	Pump runs continuously; water doesn’t leave
Pump runs continuously	Undersized pump, high water table, or failed check valve	Pump cycles without stopping
No backup power	Pump goes offline during outages	Flooding during storms when pump is most needed
Open or unsealed pit cover	Radon and moisture entry	Elevated radon test results; musty basement odor

Signs Worth Checking

• Water in the pit with no pump activation
• Pump runs but water level doesn’t drop
• Unusual grinding or rattling during pump cycles
• Rust or mineral staining on the discharge pipe or pit walls
• A musty smell that worsens in wet weather, which can indicate moisture entry through an unsealed pit
• Visible corrosion on battery backup terminals

A pump that runs constantly without clearing the pit usually points to a failed check valve (allowing expelled water to flow back into the pit), a blocked discharge line, or a pump undersized for the actual inflow.

What to Maintain Yourself

Monthly: Lift the float switch by hand to confirm the pump activates and moves water. This takes about 30 seconds and is the most reliable way to catch a failure before a storm does it for you. While you’re there, check the battery backup terminals for corrosion: white or greenish buildup on the terminals reduces the backup’s ability to hold a charge.

Annually: Clean the inlet screen at the base of the pump. Debris (silt, gravel, small stones) collects there and restricts flow or jams the impeller. Pumps that run frequently need this done more often. Pull the pump, rinse the screen, and inspect the float switch for any fouling.

Also confirm the discharge pipe terminus each spring. Ice can block it over winter, and a blocked discharge line causes the pump to run against a closed system.

Covering the pit: If your pit doesn’t have a sealed cover, fit one. Covers are inexpensive and available at hardware stores. The cover should lock or latch: open pits are a drowning hazard for small children.

Backup power: If you don’t have a battery backup unit, it’s worth considering. Power outages frequently coincide with the heavy rain events that put the most demand on the pump. A battery backup system typically costs $150–$300 and provides several hours of operation. If you’re using a portable generator during an outage, keep it at least 20 feet from the house, outside, in open air. Never run a gas-powered generator in a basement, garage, or crawlspace. Carbon monoxide accumulates quickly in enclosed spaces and is fatal.

Electrical safety: The sump pump circuit should have GFCI protection. In a wet basement environment, a standard outlet creates a shock hazard. Check whether the pump’s outlet or circuit breaker is GFCI-protected; if it isn’t, have an electrician add it.

When the Work Requires a Pro

Call a plumber or waterproofing contractor when:

• The pit has no perimeter drain system feeding into it, so the pump is working against groundwater without any upstream collection, which limits its effectiveness
• The pump fails and flooding has already occurred or is imminent
• You need to install a new pump and aren’t confident in running or modifying the discharge line
• The discharge needs to be rerouted, for example if it currently terminates too close to the foundation or near a septic system drainfield (sump discharge near a drainfield slows the wastewater treatment process and can damage the field)
• Radon levels test high and you need a mitigation system designed around the sump pit

Plumbing codes govern sump construction, cover requirements, venting, discharge lines, and alarm requirements. A licensed plumber will know what applies in your jurisdiction; a radon mitigation contractor can design a system that uses the sealed pit as the suction point.

The pump is simple equipment doing a straightforward job. Keep the pit covered, test the float monthly, and have a backup for power outages. Those three habits account for most of what goes wrong.