Sump pump keeps running: what it means and when to call a pro

How a sump pump system works

A sump pump sits in a pit (the sump or basin) at the lowest point of the basement. Drain pipes under or around the floor lead groundwater into the pit. When the water rises, a float switch turns the pump on. The pump pushes the water up through a discharge pipe and outside, and a check valve in that pipe stops the water from falling back into the pit when the pump shuts off. When the level drops, the float turns the pump off again.

So a pump that runs is not a problem in itself. The questions are how often, for how long and whether water is actually coming in.

When frequent running is normal

• During and after heavy rain or snowmelt. The soil is saturated and groundwater keeps flowing into the pit. Running every few minutes for hours or even days can be normal.
• In areas with a high water table. In parts of South Jersey, for example, groundwater sits close to the surface – the New Jersey Pinelands Commission notes that the Cohansey aquifer’s water table is generally less than 10 feet down and often reaches the surface in low areas. Homes in places like that can have pumps that cycle for weeks in a wet season.
• In spring, when the water table is typically at its highest.

If water visibly flows into the pit from the drain pipes, and the pump empties it and shuts off, the system is working. It may still be worth talking to a professional about a larger pump or a backup, because a pump that works this hard wears out faster.

When it signals a problem

These are the most common reasons a pump runs constantly or switches on and off every few seconds (“short cycling”):

• Stuck float switch. The float can catch on the side of the pit, the power cord or debris and stay in the “on” position. The pump keeps running even when the pit is empty, which can burn out the motor.
• Failed or missing check valve. Without a working check valve, the water in the discharge pipe falls back into the pit each time the pump stops, and the pump turns on again to pump the same water. You may hear a thump or a rush of water when the pump shuts off.
• Pump too small or worn out. An undersized or aging pump runs long cycles and can’t keep up in heavy rain.
• Pit too small. A small basin fills in seconds, so the pump starts and stops constantly.
• Frozen, clogged or damaged discharge line. If water can’t leave the house, the pump runs without lowering the level. In winter, discharge lines that are not sloped to drain can freeze.
• Water coming back around. If the discharge ends right next to the foundation, the same water soaks back down to the drain tile and into the pit.
• A plumbing or irrigation leak. Clean, clear water flowing in during a long dry spell can come from a leaking water line or irrigation system near the house.
• Electrical problems or a failing switch that no longer reads the water level correctly.

Safe checks you can do yourself

Safety first: a sump pit mixes water and electricity. Unplug the pump before you put your hands in the pit, and make sure it is plugged into a protected (GFCI) outlet as your local code requires.

1. Watch one full cycle. Does the water level actually drop? Does the pump shut off when the float drops? If it keeps running with an empty pit, the switch is the likely culprit.
2. Look at the float. With the pump unplugged, make sure the float can move freely and is not caught on the cord, the pit wall or debris.
3. Listen when it stops. A loud thump and water rushing back into the pit point to a failed check valve.
4. Follow the discharge pipe outside. Is water coming out? Is the end blocked, frozen or buried? Does it release the water far enough from the house that it flows away rather than back toward the foundation?
5. Check the inflow. During dry weather, see whether water is still flowing into the pit and whether it is clear. If you have public water, turn off all fixtures and watch the water meter: if it still moves, you may have a leak.
6. Clean the pit of gravel, silt and debris that can jam the float or clog the intake.

When to call a professional

• The pump runs continuously with no water coming in, or never shuts off.
• The pump hums but does not pump, trips the breaker or smells hot.
• The pit is full or overflowing even though the pump is running.
• The pump is more than several years old and has started to struggle in storms.
• Water still gets into the basement although the pump works – a sign the drainage system itself is not collecting the water.
• Your basement is finished and a failure would be expensive.

A contractor can replace the switch or check valve, install a larger pump or a larger basin, reroute the discharge line or add a second pump. According to This Old House, installing a sump pump costs about $1,400 on average, with most projects between $500 and $4,000 depending on whether a pit already exists. See sump pump installation and our cost guide.

Backups: don’t rely on one pump

Storms that flood basements often knock out the power too. The common options are:

• Battery backup pump – a second pump in the same pit that runs on a battery when the power fails or the main pump can’t keep up.
• Water-powered backup pump – uses the pressure of the municipal water supply instead of electricity. It needs city water with adequate pressure and uses water while it runs; check local plumbing rules.
• High-water alarm – an inexpensive alarm or smart sensor that warns you when the water rises too high, so you can act before it overflows.

Where sump pumps work hardest

Pumps work especially hard in areas with shallow groundwater and old drainage, such as South Jersey, homes near the creeks of Bucks and Montgomery County and the slow-draining soils of Central Jersey. If your pump runs all spring and water still gets in, read water in the basement after heavy rain.

Sources

• New Jersey Pinelands Commission: The Cohansey Aquifer
• This Old House: Sump pump cost