Short definition

Sump pump troubleshooting is the homeowner’s diagnostic decision tree when the pump won’t start, runs continuously, overheats, or makes new noises. The four most common patterns map to four root causes: a dead power circuit, a stuck float switch, a jammed impeller, and a failed check valve.

Most common symptoms

Pump won’t start. Power, float switch, or motor.

Pump runs continuously. Stuck float switch (open), failed check valve, undersized pump, or abnormal inflow.

Pump overheats. Clogged impeller, motor bearing failure, or pump-out blockage downstream.

Strange noises. Bearings going, debris in the impeller, water-hammer at the check valve, or cavitation from low water level.

Diagnostic decision tree

Work through these in order — most failures resolve at one of the first three steps.

1. Power

  • Is the GFCI tripped at the outlet or panel?
  • Is the cord plugged in (or connected to its dedicated circuit)?
  • Test the outlet with a known-good lamp or tester.
  • If a battery backup is also installed, did the AC pump’s power source fail and the backup not engage?

2. Float switch

  • Lift the float manually with a stick or broom handle. The pump should activate.
  • If the pump runs when the float is lifted but not on its own, the float is stuck.
  • If the pump runs continuously when the float is down, the switch is stuck closed.
  • Submerged tethered floats can wedge against the pit wall — reposition.

3. Impeller

  • Power off at the breaker.
  • Pull the pump up out of the pit.
  • Inspect the impeller intake; remove any debris (gravel, plastic, fabric).
  • Spin the impeller manually — it should rotate freely.

4. Discharge line

  • Verify water is exiting the discharge pipe at the outdoor termination.
  • In winter, especially eastern WA: is the discharge line frozen?
  • Outdoors: is the discharge buried or extended into a yard with no slope back?

5. Check valve

  • With the pump just shut off, water above the valve should not drain back into the pit.
  • If you can hear or see water falling back, the check valve has failed. See sump pump check valve.

6. Motor

  • If the breaker trips immediately on power-up, the motor is shorted.
  • If the pump hums but doesn’t run, the seal has failed and water is in the motor.
  • If the motor body is hot to the touch immediately after a cycle, the motor or seal is failing.

Why it matters to a homeowner

Most sump pump troubleshooting is solvable in under an hour with a flashlight and a stick. The high-stakes scenario is during a heavy rain event when the pump won’t start and water is rising — so a working baseline knowledge of these steps is what stands between a 20-minute fix and a flooded basement.

If the pump won’t start during a storm and the first three steps don’t resolve it, the safe move is to call an emergency plumber and, if possible, run a wet-vac from the pit until they arrive. Have a known-good replacement pump on the shelf for any home where the basement is finished — it’s cheaper than the response.

Common patterns and what they usually mean

  • Pump cycles every 15–30 seconds during rain → check valve failed.
  • Pump runs but discharge line is dry → discharge line frozen (eastern WA winter) or impeller jammed.
  • Pump runs constantly even in dry weather → stuck float or undersized pump for actual inflow.
  • Rumbling noise from the pit → bearings failing; replace soon.
  • Loud thump every shut-off → swing-check valve closing; replace with silent or spring check.
  • New sound after recent install or service → debris in pit; clean it out.
  • Motor hums but doesn’t pump → motor seal failed; replace pump.

Common variants and not the same as

  • Sump pump troubleshooting (clean water) vs. sewage ejector troubleshooting (solids handling) — solids handling adds different failure modes.
  • Submersible failure modes vs. pedestal failure modes — pedestal motors are exposed and fail differently. See submersible vs. pedestal entry.
  • Single-pump vs. dual-pump — in dual-pump systems, the secondary should activate when the primary fails; verify the secondary too.

Washington note

In WA, the high-stakes failure window is November through April, and almost always during a storm with a power outage. The most common combination of failures: heavy rain + power outage + a battery backup whose battery hasn’t been tested in 2 years and won’t hold charge. Annual testing in October — pour 5 gallons in the pit, kill the primary breaker, verify the backup activates and runs — catches this every time.

For homes in Spokane and eastern WA, the seasonal failure mode shifts to discharge-line freezing: the pump runs but water can’t exit. Discharge lines in unconditioned space need either insulation, a freeze-relief discharge tee, or routing that keeps the line below frost depth.