Newly installed sump pump sitting in a basement sump pit
4 components covered

Field manual · Sump / Well Pump

Residential sump pump systems: field service manual

Covers: 120 V residential submersible and pedestal sump pumps, float switches, check valves, discharge piping and DC battery backup systems

Cross-checkedBrands: Zoeller, Wayne, Liberty, Superior Pump, Basement Watchdog, Little Giant, Pentair4 components

A sump system collects groundwater in a pit and pumps it outside. The pump, float switch and check valve fail most often, and electrical supply problems are the leading cause of failures. A battery backup adds a second DC pump with its own float and an alarm controller.

Safety first

  • Unplug before reaching into the pit
  • Batteries can vent hydrogen; avoid sparks
  • Laundry water: use only floats and pumps rated for it

How it works

Water enters the pit from drain tile. When it lifts the float to the on point, the switch powers the pump; when the level falls to the off point, the pump stops.

Submersible pumps sit in the pit and are cooled by the water; pedestal pumps keep the motor on a column above the pit and use a rod-type float.

The check valve stops the water column in the discharge pipe from falling back into the pit. An anti-airlock hole between the pump and check valve lets trapped air escape so the pump can prime.

Battery backups use a 12 V DC pump on a separate float set higher than the primary; the controller charges the battery and sounds alarms for power, battery, fuse and pump-run conditions.

Components & tests

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Official manufacturer documentation

Always confirm values against the tech sheet for the exact model.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.Generic part photos (not of this brand): Newly installed sump pump sitting in a basement sump pit by Famartin, CC BY-SA 4.0

Diagnostic guides for this appliance

Guide · Sump / Well Pump

Sump pump trips the GFCI or breaker

A GFCI that trips with a sump pump is usually detecting real current leakage from a pump motor taking on water, a damaged cord or splice, or another load on the same circuit. Isolate the pump from the circuit before blaming the GFCI, and never bypass the protection on a pump in water.

4 steps ~45 minmoderate
Guide · Sump / Well Pump

Sewer or musty smell from the sump pit

A clean sump pit should not smell like sewage. Most odors come from a pit that has dried out and no longer seals the drain tile lines, stagnant water, organic buildup, or nearby plumbing traps that have dried or been siphoned. A strong, persistent sewage smell can mean a leaking sewer line near the pit.

6 steps ~30 mineasy
Guide · Sump / Well Pump

Sump pump keeps cycling when it has not rained

The most common cause is water returning from the discharge pipe through a failed or missing check valve, so the pump moves the same water again and again. Other causes are a small basin, a float set too close, a high water table or a leak feeding the pit.

4 steps ~40 mineasy

Other sump & well pumps manuals

Manual · Sump / Well Pump

Residential well pump systems: field service manual

Private-well systems with submersible or jet pumps, captive-air pressure tanks, mechanical pressure switches and constant-pressure drives (e.g. Franklin SubDrive/MonoDrive)

4 components4 common failuresGoulds, Red Lion, Franklin Electric, Pentair, Wayne, Others
Residential sump pump systems: field service manual · OnCall Tech