Short answer
If your sump pump is not working, treat the pit as electrically live and do not reach in while the pump is plugged in. Check power, the GFCI outlet, the breaker and a stuck float first. Test by pouring water in slowly and watching a full cycle. A pump that will not start, never stops or sounds rough needs a plumber. A battery backup is worth asking about.
A sump pump usually fails when it is needed most, during heavy rain or snowmelt. This guide explains how a sump pump works, how to test a sump pump, why a pump may not turn on or may run constantly, what a sump pump alarm may mean, and where the water may go. It draws on extension services, a city checklist, the US Consumer Product Safety Commission and emergency-preparedness pages. It is general information, not a substitute for your pump's manual or a licensed professional.
How a sump pump works
A sump is a pit in the basement or crawlspace floor. NDSU Extension (2013) says the pit may connect to drain tile around the footings, to the whole basement area, or only to the area right around the pit, and that the pump removes the water that drains into it. When the water rises to a set level, a float or switch starts the pump. The pump pushes water out through a discharge pipe, and when the level drops it shuts off.
NDSU describes two pump types. A pedestal pump has its motor on a column above the pit, and the motor is not meant to get wet. A submersible pump sits in the pit with its switch attached. Controls are a ball float, a sealed tethered float or a diaphragm. NDSU also says both types should have a check valve on the discharge pipe so water does not flow back into the pit. Backflow makes the pump cycle more often than needed, which shortens its life.
Electrical safety first
Water and electricity are the real danger in a wet basement.
- Wet electrical equipment. Ready.gov's flood page says not to touch electrical equipment if it is wet or if you are standing in water.
- Unplug before touching the pump. SDSU Extension's guide on flooding and sump pumps (updated April 2020) says to unplug the pump and be sure it is unplugged before touching it. The City of Ann Arbor, Michigan heads its inspection steps with the same instruction.
- GFCI protection. In a January 2011 recall notice, the CPSC said sump pumps installed without GFCI protection can pose an electric shock or electrocution hazard if touched. Ann Arbor's checklist adds that a GFCI can trip and leave the pump dead, so test the button before storms. It also notes a GFCI is generally not required on a dedicated single outlet for a sump pump. Rules depend on your local code and the age of the house, so ask an electrician about your outlet.
Our rule is simple. Never put a hand, tool or foot into the pit while the pump is plugged in or the breaker is on. If water is standing around the outlet, the panel or the pit, do not step in. Call an electrician or your electric utility. CDC's flood-safety page also lists turning off electrical power when there is standing water.
Some extension pages describe lifting the float by hand to test a dry pit. That means touching a powered pump, so we suggest the pour test below.
How to test a sump pump
- Look before you touch. Confirm the outdoor discharge pipe is not frozen or plugged and sends water away from the house (NDSU Extension).
- Check power. Make sure the pump is plugged in directly to its outlet, the breaker is on and any GFCI is working (City of Ann Arbor).
- Inspect the pit. Take off the lid if there is one and use a flashlight to look for debris and plugged inlet screens (NDSU). Do not reach in. If the pit needs cleaning, unplug the pump first.
- Pour water slowly. NDSU says to pour at about the rate water normally enters. Ann Arbor says three to four gallons is usually enough to start the pump.
- Watch a full cycle. The float should rise, the pump should start, empty the pit and shut off. NDSU says the pump should turn on and off at least twice.
- Listen. NDSU says a pump that sounds like it is pumping gravel, or a sluggish float, may mean a new pump or float is needed.
- Check the discharge. Make sure water flows freely from the outdoor end (SDSU). Ann Arbor says a small stream from a weep hole in the pipe near the pump is normal, because it prevents an air lock.
Ann Arbor recommends checking at least twice a year, preferably before the spring snow melts.
Sump pump not working: common causes
| What you see | Common causes | First checks |
|---|---|---|
| Sump pump not turning on | Unplugged cord, tripped breaker or GFCI, float stuck against the pit wall or pipe, worn motor bearings, a float switch with poor electrical contact, a pump at the end of its life | Power, GFCI test button, whether the float moves freely, then call a plumber |
| Runs but moves little or no water | Plugged inlet screen, blocked or frozen discharge, air lock from a blocked weep hole | Discharge outlet outside, weep hole (unplug first), screen and pit debris |
| Sump pump running constantly | Float that does not drop, backflow through a missing or failed check valve, discharge too close to the house so water cycles back, heavy inflow, a pump that is too small | Float movement, check valve, where the discharge ends, whether it runs in dry weather |
| Shuts off then restarts hot | Frozen or plugged discharge making the motor overheat | Discharge line; shut the pump off and let it cool |
The sources behind the table are specific. Ann Arbor says if the water rises above the pump before it turns on, or the pump does not shut off when the water drops, the sensor or another part may be defective. NDSU also says a frozen or plugged discharge pipe can overheat a pump, that most motors have thermal protection, and that submersible motors need the surrounding water for cooling. If a pump overheats, shut it off and let it cool.
On a pump that never rests, Ann Arbor says a sump pump should not have to run all the time. It suggests setting the float or pump higher in the pit, and says a larger pump may be needed if that does not help. NDSU says a one-third horsepower pump suits most houses, though more than 40 feet of outdoor discharge pipe may call for a larger one. SDSU says water discharged close to the house can seep back to the foundation and be pumped again in a loop, and recommends at least 20 feet.
Sump pump alarm and battery backup
Alarms. Alarms differ by model, so read your manual. The Ann Arbor checklist says a high water alarm should activate when the float is raised, or when water reaches the sensor on a sensor type. Depending on the setup, an alarm may also sound when the primary pump is unplugged or when the backup starts. If an alarm sounds and the pit is rising, do not wade in. Look from a dry spot, check the power and GFCI where you can do so safely, and call a plumber. If water is near electrical equipment, stay out and call an electrician.
Battery backup. CDC's flood page says to buy and install sump pumps with back-up power, and Ready.gov suggests considering a sump pump with a battery. NDSU Extension (2022) says an electric backup pump is installed in the same pit, runs only if the primary fails and is battery powered. It calls battery maintenance very important and says to test the backup the same way as the main pump. NDSU's 2013 article adds a method. Fully charge the battery, shut off power to the main pump and the backup's charger, then pour water in until the backup starts. Ann Arbor adds to check the battery water level.
Ask your plumber whether the backup shares the main pump's discharge line, since a frozen or blocked line could then stop both.
Where the water goes: discharge rules
NDSU Extension (2013) says to discharge at least 20 feet from the house, and not onto a neighbor's lot, into window wells or onto a septic drain field. It also says not to pump into a basement floor drain if you have a septic system, or into a floor drain connected to a public sanitary sewer, because added water during flooding can contribute to sewage backflow. SDSU says not to discharge into the municipal sewer, because that can overwhelm the system and cause sewage backups, and that many cities prohibit it. NDSU (2022) adds that some cities allow sanitary sewer discharge before March 31 for a fee.
This is a local rule, so ask your city's public works or stormwater office before connecting a sump to any sewer. For what happens when a sewer is overloaded, read sewage backup: what to do and who to call.
In winter, a frozen discharge line is a common reason a pump labors or overheats. Check the outlet before the first hard freeze, and see the winter plumbing and septic checklist.
Annual maintenance and when to call
Ann Arbor's checklist covers testing the GFCI, clearing debris from the pit, confirming the float moves freely, checking the weep hole, confirming a check valve is in place and the air gap is clear, and inspecting outdoor discharge points. It says to contact a licensed plumber to add a check valve if one is missing.
- Call a plumber when the pump will not start after the power checks, runs constantly, makes grinding or gravel sounds, has no check valve, or the pit shows heavy sediment. NDSU suggests that people new to sump pumps have a licensed plumber check the pump before spring thaw. For help vetting one, see how to find and vet a plumber.
- Call an electrician when the GFCI keeps tripping, a cord is damaged or the outlet is wet.
If water is already spreading, the general water-damage steps in burst pipe: what to do apply to clean water. If it may include sewage, treat it as contaminated and follow the sewage backup guide above.
What to look up where you live
- Your city public works or stormwater office: whether sump discharge to the sanitary sewer is banned, seasonal exceptions, and where the line may legally end.
- Building or permit office: whether replacing a pump or changing a discharge line needs a permit.
- State or provincial plumbing and electrical licensing boards: to confirm a plumber's or electrician's licence.
- Your insurance agent: whether your policy covers water from a failed pump or a sewer backup. Many policies treat these as separate items.
For Canadian readers. Plumbing and electrical work are regulated by each province or territory, and municipalities set their own sewer-use and drainage rules. Check your provincial regulator and your city. Costs are in Canadian dollars and cannot be compared directly with US figures.
For plumbing and drain company owners
Homeowners search for a failed sump pump during storms, when they want a company that answers the phone and is easy to find. If you want to be that company, read emergency plumber marketing and plumbing answering service. You can also book a call with LiveLeadsLane. LiveLeadsLane is a marketing practice for contractors, not a directory, and it does not take jobs or refer homeowners.
