Sump Pump Not Working: Find the Problem Before the Next Storm Does

Sump pumps are among the most neglected appliances in a home. They sit in a dark pit in the basement, doing nothing visible most of the time — which is exactly the problem. Nobody tests them until water is already rising. If you're reading this during a rain event with a wet basement, this article will help. If you're reading it on a dry afternoon and want to make sure your pump is ready, even better.

A sump pump failure during heavy rain or snowmelt causes the exact scenario it exists to prevent: basement flooding. Water damage claims from sump pump failure run into the thousands — sometimes tens of thousands — of dollars. The pump itself costs $150–$400. The math on proactive maintenance is obvious.

How a Sump Pump Works (Quick Version)

A sump pit — typically a 2-foot-diameter, 3-foot-deep plastic or concrete basin sunk into the basement floor — collects groundwater that migrates through the foundation. As water accumulates in the pit, a float switch rises with the water level. When it reaches the trigger point, the pump motor activates and pumps the water out through a discharge pipe that exits through the foundation wall or through the floor above, directing water away from the house.

There are two main types: pedestal pumps (motor sits on a pedestal above the water level) and submersible pumps (the entire unit sits in the water, more powerful and quieter). Submersibles are far more common in modern homes.

Step 1: Quick Power and Float Test

Before assuming the pump has failed, confirm the basics:

1. Check the outlet. Sump pump outlets are typically on a GFCI circuit. Find the GFCI outlet on the circuit and press the "Reset" button — a tripped GFCI is a common cause of a suddenly non-functioning pump.
2. Check the circuit breaker. Find the breaker labeled for the sump pump and confirm it's in the "On" position. If it's tripped to the middle position, switch it fully off then back on.
3. Plug another device into the pump's outlet to confirm power is reaching it. A lamp or phone charger works.
4. Pour water into the pit (2–3 gallons from a bucket) and watch whether the float rises and the pump kicks on. This is the most direct test of the complete system.
5. Manually lift the float switch (reach in and lift the float ball or tether float upward by hand). If the pump runs when you manually lift the float but doesn't trigger on its own, the float mechanism has failed.

Why Sump Pumps Stop Working: Six Common Failures

Failure 1: Float Switch Stuck or Tangled

The float switch is the most common single point of failure in a sump pump. Float tethers can become tangled in the pump discharge pipe. Ball floats can fill with water and sink rather than float. Vertical float switches can jam on the side of the pit. Any of these prevent the float from rising to trigger the pump.

Fix: open the pit cover and look at the float. Is it positioned correctly? Can it move freely up and down without obstruction? If it's tangled, untangle it and position it so there's clearance between the float and the pit walls. If the float itself has failed (the ball is waterlogged or the tether switch has burned out), replace just the float switch — a much cheaper fix than replacing the whole pump.

Failure 2: Pump Motor Burned Out

If power is present, the float moves freely, and the pump still doesn't activate — or activates but the motor hums without pumping — the motor may have seized or burned out. This is more common in older pumps (7+ years) or pumps that had to work very hard during a previous flooding event. A burned motor is a replacement situation, not a repair.

Feel the pump body (carefully, with rubber gloves if water is present). An unusually hot pump body suggests it ran dry or was overworked. A motor that hums but doesn't spin typically has a seized impeller or failed starting capacitor.

Failure 3: Clogged Intake Screen

At the bottom of the pump, there's an intake screen or filter that prevents debris from entering the impeller. Over time, this screen collects sediment, gravel, and debris from the pit. A heavily clogged screen restricts water intake so severely that the pump can't move water effectively — it runs but produces little flow.

Fix: disconnect the pump from power, remove it from the pit, and clean the intake screen with a brush and running water. Rinse the pit of accumulated sediment before replacing the pump.

Failure 4: Check Valve Failed or Missing

The discharge pipe has (or should have) a check valve — a one-way valve that prevents pumped water from flowing back into the pit when the pump shuts off. A missing or failed check valve means water flows back into the pit after every pump cycle, causing the pump to run almost continuously in a short-cycling pattern. Over time this burns out the motor.

Signs: the pump runs every few minutes even when it hasn't rained. You can hear water flowing back into the pit after the pump shuts off. Fix: install a check valve on the discharge pipe just above the pump.

Failure 5: Frozen or Blocked Discharge Line

The discharge line that carries water out of the house can freeze in winter (if routed through an unheated garage or exterior wall section) or become blocked by debris, ice, or a pest nest. A blocked discharge line causes the pump to run without actually moving water out — it pumps against a blockage until it overheats and fails.

Signs: pump runs but water level in pit doesn't drop. Inspect the discharge line from the pump to the exterior outlet. Clear any blockage. In cold climates, discharge lines should be pitched with an air gap at the exterior to prevent freezeback.

Failure 6: Pump Is Undersized for the Water Volume

Sometimes the pump works fine — it's just not powerful enough to keep up with the water coming in during a heavy rain event. If the pump is running continuously but water is still rising in the pit, the pump's gallons-per-hour capacity is insufficient for your soil's infiltration rate.

This is a sizing problem. A 1/3 HP pump handles typical residential applications. In high water table areas or locations with heavy soil water intrusion, 1/2 HP or 3/4 HP may be needed. A plumber can advise on the right size for your specific conditions.

Annual Maintenance: 15 Minutes That Could Save Thousands

1. Pour two buckets of water into the pit and confirm the pump activates and drains the pit completely.
2. Clean the pit of sediment and debris that accumulates over the year.
3. Inspect and clean the intake screen.
4. Check that the float moves freely in all positions — lift it by hand and confirm the pump runs.
5. Inspect the discharge line for blockages, kinks, or frost damage from the previous winter.
6. Test the GFCI outlet by pressing "Test" and "Reset" to confirm it's functioning.
7. Note the pump's age. If it's approaching 8–10 years, start budgeting for replacement before it fails during a storm.

The Battery Backup: The Most Important Upgrade

The two most common times a sump pump is needed are also the two most common times the power goes out: heavy rainstorms and major weather events. A sump pump without a backup is one power blip away from failing at the worst possible moment.

Battery backup sump pump systems install alongside the primary pump and activate automatically when the primary pump fails or the power cuts out. The battery runs the backup pump for 5–12 hours depending on the cycle rate, which is enough to cover most power outages.

Systems like the Wayne WSS30VN or Zoeller Aquanot are well-regarded options. A plumber can install one in a few hours. Budget $200–$500 for the unit and $150–$350 for installation. It's one of the most cost-effective insurance purchases for a basement owner in a high-water-table region.

If Your Basement Is Already Flooding

If water is actively rising in the basement: electrical safety first. Do not enter standing water if it could be in contact with energized outlets, the electrical panel, or appliances. Shut off the basement circuit breaker before entering. Use a battery-powered wet/dry vac or a gas-powered utility pump (operated outside — never use gas-powered equipment indoors due to carbon monoxide). See our basement flooding fix guide for step-by-step emergency response.

Cost of Sump Pump Repair and Replacement

Service	Estimated Cost
Float switch replacement (DIY)	$20–$50
Float switch replacement (plumber)	$100–$200
Check valve installation	$50–$150
New sump pump (submersible, 1/2 HP)	$150–$350
Sump pump installation (plumber)	$300–$600 total
Battery backup unit (installed)	$400–$800
New sump pit excavation and install	$1,500–$3,000

Frequently Asked Questions