Newly installed sump pump sitting in a basement sump pit

Install a battery backup sump pump and high-water alarm

A battery backup is a second 12 V DC pump that sits higher in the pit than the primary and runs off a charged deep-cycle battery when the primary cannot keep up or loses power. The key details are float height (backup turns on above the primary), a check valve on each pump's discharge so neither pumps back into the pit through the other, and a working alarm. Follow the kit's installation instructions for the exact tee and float positions.

Cross-checked ~150 min moderateBrands: All

Before you start

Unplug the primary pump before working in the pit; sump water and line voltage together are a shock hazard.
Lead-acid batteries vent hydrogen and contain acid: keep the battery in a lidded, non-metallic box, off the floor, with eye protection when handling.
Never lay a metal tool across the battery terminals.
Connect or disconnect the battery leads only with the charger unplugged from the outlet, as the kit instructions require.
If the pit discharge or electrical outlet needs to be changed, follow local code; a new circuit is work for a qualified electrician where required.

Diagnostic steps

Unlock all 10 steps with expected values

Full library + AI assistant + the OnCall Tech app for iPhone & Android. $34.90, one time.

Get lifetime access

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.

More sump & well pumps guides

Guide · Sump / Well Pump

Well pressure switch chattering or clicking rapidly

Chatter happens when the switch sees pressure bouncing around its set point. The usual causes are a plugged sensing port or nipple, a waterlogged or low-precharge tank, a switch mounted far from the tank, worn contacts or a differential set too narrow. Chatter burns contacts fast and stresses the motor, so fix it the same day.

8 steps ~45 minmoderate

Guide · Sump / Well Pump

Jet pump loses prime or runs without building pressure

A jet pump only works when its housing and suction line are full of water. Lost prime almost always traces to an air leak on the suction side, a leaking foot valve or check valve, a clogged foot-valve screen, or a well that has drawn down. Fix the cause, then re-prime; repeated priming alone just burns pumps.

7 steps ~60 minmoderate

Guide · Sump / Well Pump

Well pump hums, won't start or trips overload: control box test (3-wire)

On a 3-wire submersible, the start capacitor and relay in the control box are the most common surface failures and can be tested with a meter. First confirm power through the pressure switch, then test the box. If the box is good or the system is 2-wire, the problem is down the well and goes to a well contractor.

8 steps ~60 minadvanced