Why Won't My Sump Pump Turn On — or Why Won't It Stop?

Root cause

Sump pumps are usually plugged into a dedicated GFCI-protected outlet, which can trip from humidity in the pit alone — no actual fault required. A tripped breaker or a pump that's simply come unplugged (easy to nudge loose while working in a crawlspace or basement) produces the exact same symptom: nothing happens at all.

30-second check

Confirm the pump is plugged in, then check both the GFCI outlet it's plugged into and the breaker panel for a trip.

Tools & materials

None required.

Step-by-step

1. 1 Confirm the plug is fully seated in the outlet.
2. 2 Press “Reset” on the GFCI outlet the pump is plugged into.
3. 3 Check the breaker panel for a tripped breaker and reset it.
4. 4 Test the pump by pouring a bucket of water into the pit to trigger the float.
5. 5 If the GFCI trips again immediately, stop — that points to a wiring or motor fault, not a nuisance trip.

Root cause

The float switch is what tells the pump to turn on as water rises and off once it drops. If it's tangled in the pump's power cord, wedged against the side of the pit, or jammed by debris, it can get stuck in either position — permanently off (pump never starts) or permanently on (pump runs constantly, even with a nearly empty pit).

30-second check

Lift the pit lid and watch the float arm or ball as you pour water in — it should rise and fall freely without catching on the cord, the pump body, or the pit wall.

Tools & materials

None required, occasionally a pair of gloves for clearing debris.

Step-by-step

1. 1 Unplug the pump before reaching into the pit.
2. 2 Untangle the float switch from the power cord if it's caught.
3. 3 Reposition the pump so the float has clear room to move in every direction.
4. 4 Clear any debris (dirt, small stones, sump liner fragments) blocking the float's path.
5. 5 Plug the pump back in and test with a bucket of water.

Root cause

The intake screen at the base of the pump keeps debris out of the impeller, but it can clog with sediment and grit over time, restricting flow even while the motor runs fine. Outdoors, the discharge line can freeze solid in cold weather, which has the same effect — the pump runs but water has nowhere to go.

30-second check

Listen for the motor running without water visibly leaving the pit, or check the outdoor discharge point for ice during cold weather.

Tools & materials

Garden hose, a stiff brush, hair dryer or heat tape for a frozen line (never an open flame).

Step-by-step

1. 1 Unplug the pump and lift it out of the pit.
2. 2 Clear the intake screen of debris with a brush and rinse with a hose.
3. 3 Check the discharge line outdoors for a visible ice blockage.
4. 4 If frozen, thaw gently with a hair dryer or heat tape — never an open flame near a plastic pipe.
5. 5 Reinstall the pump and test with a bucket of water.

Root cause

The check valve on the discharge line stops water from flowing back down into the pit after the pump shuts off. When it fails, that backflow immediately re-triggers the float, and the pump ends up turning on and off every few seconds — which wears out the motor far faster than normal use.

30-second check

Watch the pump cycle — if it's turning on and off repeatedly within a short window rather than running a normal cycle and resting, the check valve is the likely cause.

Tools & materials

Replacement check valve matching your discharge pipe diameter ($15–40), pipe wrench or PVC cement depending on your line's material.

Step-by-step

1. 1 Unplug the pump before working on the discharge line.
2. 2 Locate the check valve, usually a few feet up the vertical discharge pipe.
3. 3 Note the flow-direction arrow on the old valve before removing it.
4. 4 Install the new valve in the same orientation, matching pipe diameter.
5. 5 Restore power and test with a bucket of water, watching for a normal on/off cycle.

Root cause

During sustained heavy rain, a pump running frequently or even near-continuously for a few hours isn't necessarily broken — it may just reflect genuinely elevated groundwater around the foundation. This is worth distinguishing from a real fault before you start replacing parts.

30-second check

Confirm the pump is actually removing water each cycle (the pit level visibly drops) and that this only happens during or right after heavy rain — if so, this is very likely normal operation, not a malfunction.

Tools & materials

None — monitoring only.

Step-by-step

1. 1 Watch one full cycle: does the water level in the pit actually drop when the pump runs?
2. 2 Note whether frequent cycling coincides with heavy rain or snowmelt specifically.
3. 3 If cycling continues for days after weather clears, that's no longer normal — revisit the check valve and float switch causes above.
4. 4 If this happens every heavy rain, a larger pump or a second backup pump may be worth considering rather than a repair.

Root cause

Sump pump motors typically last 7–10 years with normal use. A motor that hums without spinning, trips the GFCI repeatedly even after a clean reset, or simply never starts despite confirmed power is usually past the point of a simple fix — and at that age, replacement is normally more cost-effective than repair anyway.

30-second check

The pump has power (confirmed via Cause 1) and the float moves freely (confirmed via Cause 2), but it still won't run — or it trips the GFCI again immediately after a clean reset.

What a professional actually does

A plumber tests the motor's electrical draw and windings, replaces the pump outright if it's failed or aging, checks the dedicated circuit and outlet for damage, and confirms the backup battery or water-powered backup system (if installed) is also functioning.