How to test a sump pump

A sump pump sits quietly in a pit in your basement or crawlspace for months, then has to work perfectly during the worst storm of the year. The only way to know it will is to test it. It takes about five minutes.

The bucket test, step by step

1. Check the power. Make sure the pump is plugged in. If there are two plugs in a "piggyback" arrangement, that is the float switch and the pump; both must be connected.
2. Fill a bucket with about 5 gallons of water.
3. Pour slowly into the pit. Watch the float (a ball on an arm or a cylinder on a vertical rod) rise with the water.
4. The pump should switch on by itself before the water gets near the top of the pit.
5. Watch it empty the pit within a few seconds to a minute, then shut off on its own.
6. Go outside and confirm water is coming out of the discharge pipe and flowing away from the house.

What the results mean

• Nothing happens: check the outlet (see the GFCI note below), the breaker and whether the float is stuck against the pit wall or snagged on debris.
• Motor hums but no water moves: the impeller may be jammed or the intake clogged. Unplug the pump before inspecting.
• Pump runs but won't shut off: the float switch is stuck or failing.
• Water flows back into the pit after shutoff: the check valve on the discharge pipe isn't closing. A short "thunk" when the pump stops is normal; a steady return flow is not.
• Loud grinding or rattling: worn bearings or debris in the impeller.

The hidden problem: the GFCI outlet

Electrical codes generally require GFCI protection for basement and crawlspace receptacles, and that often includes the sump pump outlet. A GFCI protects against shocks, but it can also trip silently from moisture or a minor fault, leaving the pump without power. You won't know until the basement floods.

Check whether your pump is on a GFCI outlet or a GFCI breaker. If it is, test the pump regularly, and consider a high-water alarm: an inexpensive battery-powered device that sounds when water rises in the pit. Some Wi-Fi models send a phone alert. If the outlet keeps tripping, read why GFCI outlets keep tripping and have an electrician look at it rather than removing the protection.

Yearly cleaning

1. Unplug the pump.
2. Remove the pit cover and scoop out gravel, silt and debris from the bottom.
3. Clean the intake screen on the pump if it has one.
4. Make sure the float moves freely through its full range.
5. Check that the discharge line outside isn't crushed, frozen or blocked, and that it drains far enough from the foundation.
6. Plug back in and run the bucket test.

Backup options

Power often goes out during the same storms that send water into the pit. Two common safety nets:

• Battery backup pump: a second pump in the same pit that runs on a deep-cycle battery when the main one can't. Test it too, and replace the battery as the manufacturer recommends.
• Water-powered backup: uses municipal water pressure to pump the pit, with no battery. Only works where you have city water with adequate pressure, and may require a backflow preventer by code.

How often to test

Every three to four months is a good routine, plus right before your local rainy season or spring thaw. If the pump runs often during wet weather, it is already testing itself, but still listen for changes in sound and run time. Most primary pumps last somewhere around 7 to 10 years, so plan for replacement before an old pump fails at the worst moment.