If the motor runs but the water level does not fall, the problem is in the water path or the pump is no longer producing useful flow. A blocked or frozen discharge, a valve problem, an obstructed intake, air lock on some models or an internal pump fault can look similar from above the pit.
Last reviewed September 24, 2026.
Follow the water path
| What you observe | Possible explanation | Low-risk observation | Next step |
|---|---|---|---|
| Motor sound; no outdoor discharge | Blocked/frozen discharge, closed/stuck valve, failed pump or disconnected pipe | Look at the known discharge outlet from a stable, dry exterior location. | If the pit rises, call urgently and have the full discharge route checked. |
| Motor hums but does not sound like a normal run | Jammed/failed pump, obstructed intake, low-voltage/control problem | Record the sound and whether the water level changes at all. | Professional service; do not open the pump while troubleshooting. |
| Some water leaves, but pit level barely falls | Inflow exceeds flow, restriction, excessive lift/head, wear or undersizing | Time the water-level change and compare it with visible inflow. | Provide pump model, vertical lift and discharge route to the technician. |
| Water falls back immediately after shutdown | Missing, reversed, stuck or leaking check valve is plausible | Observe the return surge and shutdown sound. | See check-valve symptoms. |
| Problem began during freezing weather | Frozen exterior discharge is plausible | Inspect only accessible exterior pipe from safe ground. | Do not use flame or unsafe heating; call service if blocked. |
About air lock and vent holes
Some pump and discharge arrangements use a manufacturer-specified anti-airlock or vent-hole detail. Others do not use the same location or instruction. Pentair’s troubleshooting guidance, for example, describes an anti-airlock hole for certain situations, but that is not a universal instruction to drill an unknown system. Check the exact pump manual before modifying pipework.
Information that speeds up service
- Pump manufacturer/model and approximate age
- Whether the sound is a normal motor run or only a hum
- Whether any water exits outdoors
- Vertical rise from pump to discharge and obvious long horizontal runs
- Whether the problem began after freezing weather, a storm or recent plumbing work
- Whether water falls back into the pit after shutdown
Sources and scope
Use the manual for your exact pump, controller, valve and backup system when it differs from general guidance.
- CDC — Reentering Your Flooded Home — Electrical and reentry safety around standing water.
- Pentair — Sump Pump Troubleshooting FAQ — Manufacturer troubleshooting information for float, flow, noise, check valves and common failure modes.
- Zoeller — Product Support — Manufacturer manuals and model-specific support.