Sump Pump Not Working? Step-by-Step Troubleshooting Guide
A sump pump that fails during a heavy rainstorm is one of the fastest paths to a flooded basement. Before that happens, work through this diagnostic sequence. Most failures are one of five causes — and two of them you can fix in under 10 minutes.
The Quick Test
Before anything else: pour a 5-gallon bucket of water slowly into the sump pit. Watch whether the float rises freely and the pump activates within 10–15 seconds. This single test confirms whether the pump works at all, and gives you a starting point for diagnosis.
Failure Mode 1: Pump Does Nothing (No Sound, No Hum)
The motor isn't getting power.
Check in this order:
The reset button: Many sump pumps have a thermal overload reset button (often red or orange) on the pump body or the float switch. Press it firmly until it clicks. This trips automatically when the motor overheats or overloads.
The GFCI outlet: Sump pumps should be plugged into a dedicated GFCI-protected outlet. The GFCI outlet has two small buttons on its face — "Test" and "Reset." Press Reset. GFCI outlets trip silently and are often overlooked.
The circuit breaker: Go to your electrical panel. Find the breaker for the sump pump circuit and flip it fully OFF, then back ON.
The power cord: Make sure the pump is actually plugged in. This is obvious, but the cord can be knocked loose during basement work.
If the pump is still dead after all four checks, the motor has burned out and the unit needs replacement.
Never use an extension cord with a sump pump. Voltage drop can burn out the motor and voids most warranties.
Failure Mode 2: Pump Hums But Won't Move Water
The motor is getting power but the impeller (the spinning pump wheel) is jammed or seized.
Check:
- Unplug the pump
- Remove it from the pit
- Check the impeller at the base of the pump — clear any gravel, debris, or silt with a stiff brush
- If the impeller shaft is seized (won't turn by hand), the motor bearings are likely failed — replacement is required
If the impeller spins freely but the pump still doesn't move water after cleaning, check the discharge line (see below).
Failure Mode 3: Float Switch Stuck or Mispositioned
The float switch triggers the pump when water rises to a set level. If the float is tangled against the pump body, the pit wall, or a cord, the pump won't activate even when the pit fills.
Test: Lift the float manually. The pump should start immediately. If it does, the float is getting stuck.
Fix:
- Ensure the float can swing freely without hitting the pump, discharge pipe, or pit walls
- If necessary, reposition the pump in the center of the pit or use zip ties to route cords away from the float path
- If the float switch itself is defective (pump doesn't start even when float is manually lifted to trigger position), replace the float switch: $35–$70 in parts
Failure Mode 4: Pump Runs But Water Level Doesn't Drop
The pump is running, but water isn't leaving the pit.
Check the discharge line:
- Disconnect the discharge line at the pump outlet
- Look and feel for obstructions — packed debris, a frozen section (in cold climates), or a check valve stuck closed
- In winter, the exterior discharge outlet can freeze shut, causing the pump to run against a blocked line continuously — this burns out the motor within hours
Fix: Clear the blockage. In cold climates, install a freeze-guard fitting at the exterior discharge outlet to prevent ice blockage.
Failure Mode 5: Pump Runs Continuously
If the pump runs nonstop without cycling off:
- The float switch may be stuck in the "on" position
- The pit may have more water inflow than the pump can handle (undersized pump)
- The discharge line may have a partial blockage forcing the pump to work harder without fully draining the pit
If the pump has been running for more than 20–30 minutes without cycling off, unplug it to prevent motor burnout. A continuously running pump against a blocked discharge can fail within hours.
Replacement Costs (2026)
| Component | Cost |
|---|---|
| Float switch only | $35–$70 (parts) |
| Submersible pump unit only | $100–$400 |
| Pedestal pump unit only | $60–$170 |
| Full replacement (installed) | $309–$754 |
| Most homeowners pay | ~$530 installed |
| Battery backup add-on | $160–$500 |
Source: Angi, HomeGuide 2026
Submersible pumps (motor is in the water) typically last 7–10 years. Pedestal pumps (motor mounted above the pit) can last 25 years because the motor runs cooler.
When to Call a Plumber
- Motor burned out (no response after all power checks)
- Impeller is seized
- Discharge line requires excavation or replacement
- You want a battery backup system installed (critical for power-outage floods)
Annual maintenance tip: Test your sump pump every spring before rainy season and every fall before winter. The 5-gallon bucket test takes 2 minutes and could save you from a $10,000–$50,000 flood.
Key Takeaways
- Start with the 5-gallon bucket test to confirm whether the pump activates at all
- Dead pump: check reset button, GFCI outlet, circuit breaker — in that order
- Humming but not pumping: clear the impeller screen
- Float stuck: ensure the float swings freely without obstruction
- Running but not draining: check for a blocked or frozen discharge line
- Full replacement costs $309–$754 installed; most pay around $530