Short answer
If the pump runs but the pit stays full, water is not exiting the discharge line. Common causes: clogged or frozen outlet, failed check valve letting water slide back, corrugated pipe with trapped debris, or insufficient pump head for the pipe run. The motor burns out while the basement still floods.
Dive deep
A sump system is only as good as its weakest link after the impeller. We see discharge lines crushed by landscaping, plugged with rodent nests, or iced shut at the termination during cold snaps. Cheap check valves slam open and closed, causing water hammer and eventually sticking open—half the pumped volume returns to the pit each cycle.
Corrugated flex pipe on discharge is a repeat offender: ribs hold sediment, low spots hold water that freezes, and snakes cannot clear them reliably. We run solid Schedule 40 PVC with proper slope, exterior air gap or IceGuard-style freeze relief, and a quality quiet check valve sized for the pump curve.
Total Dynamic Head matters: long runs, elbows, and vertical lift require a pump matched to the system. An undersized pump spins in the pit without moving water to the street. Diagnosis starts at the outlet and works backward— not by swapping the pump blindly.
Maintenance is simple but neglected: verify the outlet at the street or daylight point every fall, before leaf debris and freeze season. A five-minute check prevents the overnight flood that burns out a good pump.
Dual pumps in a sealed basin share discharge through a common check valve assembly sized for combined flow—another detail NDS-certified installs get right and handyman swaps miss.
Discharge lines that daylight downhill still need critter guards at the outlet—bees and rodents nest in open pipes and block flow silently until the next atmospheric river.
When it applies
- Pump audible every few minutes but pit level unchanged
- Discharge appears at the outlet briefly then stops while pump still runs
- Recent landscaping or paving buried the discharge termination
- Corrugated black pipe visible on the exterior wall exit
When it does not
- Pump never runs—incoming groundwater exceeds pump capacity or float is stuck
- Water enters faster from a broken supply line, not groundwater
- Basin seal so tight that venting issues mimic pump failure—rare but checked
What we do next
We test pump curve, inspect valve and line, replace corrugated with PVC, and verify termination clear of blockage and freeze risk.
