A sump pump check valve is one of the smallest parts of your sump system, and one of the most overlooked. When it works, you never think about it. When it fails, your pump can end up pumping the same water over and over until it wears itself out.
Here is the short answer. A sump pump check valve is a one-way valve on the discharge pipe that stops water from draining back into the pit after the pump shuts off. A failing valve usually shows up as a loud thud, a pump that cycles on and off too often, or water you can hear rushing back into the pit.
I am Dylan with Better Basements & Waterproofing. We install and service sump pumps throughout Portland, Eugene, and Vancouver, and we put a check valve on every discharge line we install. Here is what yours does, how to spot a bad one, and what to do about it.
What a Sump Pump Check Valve Does
When your sump pump runs, it pushes water up the discharge pipe and out of the house. When the pump shuts off, the water still sitting in that vertical pipe wants to fall straight back down into the pit.
The check valve stops that. Water pressure from the pump pushes the valve open, and the valve closes when the pump stops. Without it, the water in the pipe drains back into the pit, raises the water level, and can trigger the pump again. Your pump ends up moving the same water twice.
Pump manufacturers recommend check valves for exactly this reason. Boshart, a check valve maker, explains that a check valve reduces short cycling and helps extend the life of the sump pump.
Where the Sump Pump Check Valve Should Be Installed
The valve belongs on the discharge pipe, a short distance above the pump, usually near floor level or just above the top of the pit. That keeps it easy to reach for inspection and replacement.
Most valves have an arrow molded into the body. The arrow should point up, in the direction the water flows out of the house. A valve installed upside down will block flow entirely.
Many pump manufacturers also call for a small weep hole drilled in the discharge pipe between the pump and the check valve. It lets trapped air escape so the pump does not air-lock. Follow your pump manufacturer’s instructions on this.
Types of Sump Pump Check Valves
Swing (gravity) check valves are the most common type on residential sump pumps. A flapper swings open when the pump runs and drops closed when it stops.
Spring-loaded check valves, often sold as quiet or silent check valves, use a light spring to close the flapper before the water column slams it shut. They are designed to reduce the loud bang that some swing valves make.
Ball check valves use a ball that seats against an opening to stop backflow.
The right type depends on your pump, pipe size, and how your system is set up.
5 Honest Signs Your Sump Pump Check Valve Is Failing
Sign 1: A loud thud or bang when the pump shuts off. With a swing valve, the falling column of water can slam the flapper closed. Some noise is normal for gravity valves. A sudden change, or a bang loud enough to shake the pipe, is worth a closer look.
Sign 2: You hear water rushing back into the pit. If water pours back down the pipe every time the pump stops, the valve is not sealing.
Sign 3: The pump cycles on and off too often. When backflow refills the pit, the float rises again and the pump restarts. Read our guide on how often a sump pump should turn on to know what normal looks like during Portland’s rainy season.
Sign 4: The pump seems to run constantly. A failed check valve is one of the causes we cover in our guide on why a sump pump runs constantly.
Sign 5: Leaks, cracks, or corrosion at the valve. Look for drips at the rubber couplings, cracks in the valve body, or mineral crust around the joints. Surface corrosion on the discharge pipe or check valve is often a sign of wear on the system as a whole.
How to Check Your Sump Pump Check Valve
Make sure the pump is plugged into a working GFCI outlet, and keep your hands out of the water while it is powered.
Slowly pour a bucket of water into the pit until the pump turns on. Stay close and listen as it shuts off. A clean shutoff with the water staying in the pipe is a good sign. Water draining back, a hard bang, or the pump restarting within seconds points to a valve problem.
Our full guide on how to test a sump pump walks through the complete test, including the discharge line outside.
Repair, Replace, or Replace the Pump?
A check valve is usually an inexpensive part, and replacing a failed one is a common repair. If the valve has been letting water back into the pit for a long time, though, the pump has been working harder than it should.
If your pump is older or has been short-cycling for a while, check its age before deciding. Read how long a sump pump lasts. Replacing a valve on a worn-out pump only delays the next failure.
Frequently Asked Questions About the Sump Pump Check Valve
Does every sump pump need a check valve?
Most residential sump pump systems should have one. Without it, water in the discharge pipe drains back into the pit after every cycle, making the pump run more often.
Why does my sump pump check valve make a loud noise?
Swing valves can bang when the column of water slams the flapper closed. A spring-loaded quiet check valve is designed to reduce that noise.
How long does a sump pump check valve last?
It depends on the valve, water conditions, and how often the pump runs. Inspect it every time you test your pump, and replace it when you see leaks, cracks, or backflow.
Can a bad check valve burn out my sump pump?
A failed valve can cause short cycling, and frequent starts put extra wear on the pump motor over time.
Get Your Sump Pump System Checked
If your sump pump check valve is banging, leaking, or letting water back into the pit, we will inspect the valve, the pump, and the discharge line and tell you exactly what needs attention.
Learn more about our sump pump service
Schedule your free sump pump inspection here
Better Basements & Waterproofing serves Portland, Eugene, Vancouver, and surrounding communities in Oregon and Washington.
