Quick answer
A plumbing check valve is a one-way valve that lets water or wastewater flow in only one direction and closes automatically, using a hinged flap, spring-loaded disc or ball, when flow stops or tries to reverse, so the pipe cannot drain backward.
In homes it holds water in a well line so the pump does not restart, stops pumped sewage or sump water from falling back into the pit, and can turn the house supply into a closed system that needs an expansion tank.
Quick facts
The key facts about Plumbing Check Valve, with sources:
- Job
- Allows flow one way; blocks reverse flow 1
- Jet pumps
- Suction pipe needs one to hold prime 3
- Pump discharge (CA code)
- Accessible backwater or swing check, plus a gate or ball valve 4
- Supply side effect
- A check valve on the supply calls for an expansion tank (CA code) 6
- Failure sign (well)
- Pump runs nonstop or pressure drops with taps off 2
Key takeaways
- A check valve is plumbing’s one-way door: flow pushes it open, reverse flow slams it shut.
- Homes with wells, sump pumps, ejector pumps or grinder pumps rely on them every cycle.
- A failed check valve shows up as a pump that short-cycles, runs nonstop or loses prime.
- Adding a check valve to the water supply traps heated water’s expansion, so codes call for an expansion tank.
- A simple check valve is not a certified backflow preventer for drinking water protection.
What a check valve does without anyone turning it
Most valves in a house need a hand on a handle. A check valve works alone. Water moving the right way pushes its flap, disc or ball off the seat. When flow stops, gravity, a spring or the back-pressure of the water itself presses the closing part back onto the seat.
That simple job solves a set of household problems. In a private well, Clemson Cooperative Extension lists the check valve among the main well components because it prevents water from flowing back into the well 1.
On pumps that lift sewage or groundwater, it keeps the column of water in the discharge pipe from dropping back into the pit after each cycle 4.
You will also hear it called a non-return valve or one-way valve. A foot valve is a check valve with a strainer, set at the bottom of a suction pipe.
Check valve vs. backflow preventer
A plain check valve stops reverse flow but is not tested or approved as protection for drinking water. A backflow prevention device is a listed assembly, often with two checks and test ports, chosen for the hazard. Do not swap one for the other.
How a check valve opens and closes during a pump cycle
Using a sump, ejector or well pump as the example.
- Pump starts: Pressure from the pump pushes the flap or disc open and water moves through.
- Steady flow: The valve stays open as long as forward flow continues.
- Pump stops: Flow slows to zero, and the water in the pipe starts to fall back.
- Valve seats: The closing part drops or springs onto its seat and seals.
- Column held: The pipe stays full, so a well system holds pressure and a sump or ejector pit does not refill from its own discharge 24.
- Pump pushesValve opens
- Forward flowValve stays open
- Pump stopsWater begins to fall back
- Valve closesPipe stays full 2
- Back to step 1
Source: [2]
Which check valve types homes use
| Type | How it closes | Common home use |
|---|---|---|
| Swing check | A hinged flap swings shut | Named in California’s code for ejector and pump discharge lines 4 |
| Spring (in-line) check | A spring pushes a disc or poppet shut | Well lines, sump discharges, appliance supplies |
| Ball check | A ball rolls or floats onto a seat | Some sump and ejector discharges |
| Check valve in the pump | Built into the pump or riser pipe | Submersible well pumps 2 |
| Foot valve | Check valve with a strainer at the pipe inlet | Jet pump suction lines, to hold prime 3 |
| Backwater valve | A flap in a building drain or sewer | Keeps sewer backups out; a separate code product 7 |
Example: the pressure-hold test on a well system
Nebraska Extension describes a simple way to tell if a well system’s check valves are working 2. Clemson gives a sample switch setting for context 1.
| Step | What you see | What it means |
|---|---|---|
| Let the pump fill the tank and stop | Gauge at the cut-out pressure, for example 50 psi on a 30–50 setting 1 | Starting point |
| Shut off water to the house; use no water | Gauge holds steady | Check valves are working and there are no leaks in the lines 2 |
| Same test | Gauge drops | A leak in the line to the house, or a check valve problem 2 |
| Watch the pump light, if fitted | Pump runs continuously | A check valve in the pump or riser may be stuck open, or a line is broken 2 |
Nebraska Extension says a licensed professional should do the repair, which may mean replacing the check valve or fixing a leak 2. A soggy patch of yard between the well and the house points to a broken line rather than a valve 2.
Where check valves sit in a house
The diagram below maps the usual spots. Well systems: in or above a submersible pump, in the riser pipe, or near the pressure tank 2. Jet pumps use one on the suction pipe to hold prime 3. See our well pump page.
Sump, sewage ejector and grinder pumps: on the vertical discharge pipe just above the pit, usually with a shutoff valve above it.
California’s code requires an accessible backwater or swing check valve and a gate or ball valve on ejector and pump discharge lines, with the gate or ball valve on the discharge side 4.
For grinder pumps it requires a check valve and a fullway shutoff on the discharge 5.
Water supply: some meters, pressure-reducing valves and backflow assemblies hold pressure one way. California’s code treats any check valve, backflow preventer or other normally closed device that stops pressure escaping back to the main as making a system that needs an expansion tank 6.
- Submersible well pump or riserKeeps water from draining back into the well 12
- Jet pump suctionCheck or foot valve holds the prime 3
- Sump pump dischargeStops pumped water falling back into the pit
- Ejector pump dischargeAccessible swing or backwater check plus a shutoff (CA code) 4
- Grinder pump dischargeCheck valve and fullway shutoff (CA code) 5
- Water supplyMeters, PRVs and backflow assemblies can close the system 6
What check valves do for a home
Each location in the diagram above solves a specific problem, and each adds a part that can fail.
Benefits
Trade-offs
- Can stick open from debris or wear 2.
- Can slam shut and cause water hammer on some lines.
- Traps thermal expansion on the supply side 6.
- Adds some resistance to flow.
What a check valve will not do
A check valve is not a shutoff valve. It cannot isolate a pump for service, which is why codes pair it with a gate or ball valve on pump discharges 45.
It is also not an approved way to protect drinking water from cross-connections; that takes a listed backflow assembly matched to the hazard.
It also does not stop sewer backups through house drains by itself. That job belongs to a backflow or backwater device built for sewers, which California’s code covers separately and requires to meet ASME A112.14.1 or IAPMO IGC 305 7.
What makes check valve replacement cheap or costly
We do not print prices, because fair numbers need dated local quotes. A check valve itself is a modest part. The cost of replacing one depends almost entirely on where it is.
A sump pump discharge check valve is usually reachable. A check valve inside a submersible well pump or riser means pulling the pump from the well, which Nebraska Extension notes is professional work 2.
Other drivers: pipe size and material, whether a shutoff valve or union must be added for future service, after-hours calls, and whether a related expansion tank is also needed 6. Our plumbing cost guide explains how these add up.
We found no independent lifespan figure for residential check valves that we could verify; debris, sand and cycling frequency all shorten it.
How a check valve is installed on a pump discharge
This is plumber work in most places. The order follows California’s discharge-line rule 4.
- Pick a valve rated for the job: clean water, sump water or sewage, and the pipe size.
- Mount it with the flow arrow pointing away from the pump.
- Place the check valve where it stays accessible for inspection and repair 47.
- Add a gate or ball valve on the downstream side of the check valve 4.
- Use pressure-rated pipe for the discharge 4.
- Run the pump several cycles and confirm the valve closes without backflow or banging.
Keeping check valves working
- On a well, watch the pressure gauge with water off; it should hold steady 2.
- Listen for a sump or ejector pump restarting right after it stops, a sign water is falling back.
- Have sediment-heavy well systems checked; grit is a common reason valves stick.
- Keep the shutoff valve above a pump check valve working so a plumber can service it.
- If you add any one-way device to the supply, ask whether an expansion tank is needed 6.
Warning signs and when to call a plumber
- Well pump runs nonstop, or pressure drops when nothing is on 2.
- Jet pump loses prime and runs without moving water 3.
- Sump or ejector pump restarts seconds after shutting off.
- Loud bang when a pump stops (water hammer at the valve).
- Water heater relief valve dripping after a new check valve or PRV went in 6.
Do not remove a check valve to fix a problem
Taking out a check valve can let sewage fall back into a basin, drain a well line or defeat backflow protection. Leave removal and replacement to a licensed plumber.
Pumps sit next to water and electricity: shut off power at the breaker before anyone touches a pump or its piping, and stay out of standing water near a powered pump.
A failed pump check valve can burn out a pump or flood a pit. Call for sump pump and basement water service or emergency plumbing if water is rising.
Code rules involving check valves
Pump discharge (2025 California Plumbing Code §710.4, UPC-based): discharge lines from ejectors and pumps must be pressure-rated and have an accessible backwater or swing check valve and a gate or ball valve, the gate or ball valve on the discharge side; gate or ball valves in drainage piping must be fullway type 4.
Grinder pumps (§710.12.1): a check valve and a fullway shutoff valve on discharge piping of at least 1¼ inches 5.
Thermal expansion (§608.3): a water system with a check valve, backflow preventer or other normally closed device that keeps building pressure from dissipating back to the main must have an approved, listed, sized expansion tank 6.
Backwater valves (§710.6): must be accessible and meet ASME A112.14.1 or IAPMO IGC 305 7. IPC states use other section numbers; private wells also fall under state well rules. Rules checked 2026-10-13.
How a check valve differs from backflow, foot and gate valves
| Valve | Purpose | Operated by |
|---|---|---|
| Check valve | One-way flow | Flow itself |
| Backflow prevention assembly | Protects drinking water from contamination | Flow; tested on a schedule |
| Foot valve | Holds prime at a suction inlet 3 | Flow |
| Backwater valve | Keeps sewer backups out of a building 7 | Flow |
| Gate or ball valve | Shuts off flow for service 4 | A person |
| Pressure-reducing valve | Lowers incoming pressure | Spring setting |
Check valve myths that cause pump trouble
- Myth A check valve is a backflow preventer.
- Reality Approved backflow assemblies are listed devices chosen for the hazard; a plain check valve is not one.
- Myth Check valves never need service.
- Reality Nebraska Extension lists a stuck check valve as a cause of a pump that runs continuously 2.
- Myth Any direction works.
- Reality Flow arrows matter; installed backward, the valve blocks flow.
- Myth A check valve can isolate a pump.
- Reality Codes pair it with a gate or ball valve for that 4.
- Myth Adding a check valve to the supply has no side effects.
- Reality It can create a closed system that needs an expansion tank 6.
Wells, basements and local codes
Where you live decides which check valves you have. Rural homes on private wells depend on them in the pump and riser, and in Nebraska the maintenance is done by a state-licensed professional 2.
Homes with basements in wet regions rely on sump and ejector discharge checks. Code details vary: California and other UPC states follow §710.4 4; IPC states have their own sections. Ask your building department before changing a pump discharge.
How to tell if a check valve is your problem
Suspect the check valve when a pump restarts too soon, runs too long or loses prime, or when a well gauge falls with every tap closed. Rule out leaks first, because they cause the same signs.
Next step: on a well, do the pressure-hold test above. On a sump or ejector, watch one full cycle and listen for water rushing back.
Read the arrow
Every check valve has a flow arrow cast or printed on the body. When you photograph your pump setup for a plumber, include the arrow. It answers the first question they will ask.
Questions about Plumbing Check Valve
Do I need an expansion tank if I have a check valve?
Often, yes, if the check valve is on the house water supply.
The 2025 California Plumbing Code says a system with a check valve, backflow preventer or other normally closed device that keeps pressure from escaping back to the main must have a listed, sized expansion tank.
A check valve on a sump or ejector discharge does not trigger that rule, because it is not on the drinking water side.
How do I know if my check valve is bad?
Common signs are a well pump that runs nonstop, well pressure that drops with every tap off, a jet pump that loses prime, or a sump pump that restarts seconds after stopping. Leaks cause similar signs, so have them ruled out first.
Do sump pumps need a check valve?
Most installations use one on the discharge pipe so the water in the pipe does not fall back into the pit each time the pump stops. That saves the pump from pumping the same water twice. Follow the pump maker’s instructions and local code.
Where is the check valve on a well pump?
On submersible systems it may be built into the pump or installed in the riser pipe, and some systems add one near the pressure tank. On jet pumps, the suction pipe needs a check valve or foot valve to hold prime. A well professional can tell you which your system has.
Is a check valve the same as a backflow preventer?
No. A plain check valve stops reverse flow but is not approved to protect drinking water. A backflow prevention assembly is a listed device chosen for the specific hazard and often tested on a schedule. Codes treat them differently.
Why does my water heater relief valve drip after a check valve was installed?
The check valve can trap the extra volume of heated water, raising pressure. California’s code requires an expansion tank on systems with a check valve, backflow preventer or similar device that stops pressure escaping to the main. Have a plumber check pressure and the tank.
Why does my check valve bang?
A loud bang when a pump stops is usually water hammer as the valve slams shut against a falling column of water. Valve type, size and placement affect it. A plumber can suggest a different check valve design or other fixes.
Which way does a check valve go?
The arrow on the body points in the direction water should flow, away from the pump. Installed backward, it blocks flow completely. Codes also call for a shutoff valve on the downstream side of a pump discharge check valve so it can be serviced.
Sources
- Clemson Cooperative Extension, Residential Drinking Water Well: Well Components (1st in Series), retrieved .
- Nebraska Extension, Private Drinking Water Wells: Operation and Maintenance of Mechanical Components (G2153), retrieved .
- Nebraska Extension, Private Drinking Water Wells: Water Distribution System Components (G2152), retrieved .
- 2025 California Plumbing Code §710.4 Discharge Line, as published by GoCodeBook, retrieved .
- 2025 California Plumbing Code §710.12 Grinder Pump Ejector, as published by GoCodeBook, retrieved .
- 2025 California Plumbing Code §608.3 Expansion Tanks and Combination Temperature and Pressure-Relief Valves, as published by GoCodeBook, retrieved .
- 2025 California Plumbing Code §710.6 Backwater Valves, as published by GoCodeBook, retrieved .
Expert review
Written by the HyrePlumber Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Well roles, the pressure-hold test, stuck-valve symptom and jet pump prime from Nebraska Extension G2152 and G2153; backflow-into-well role and the sample switch setting from Clemson Extension.
Discharge, grinder, expansion-tank and backwater rules from 2025 California Plumbing Code §§608.3, 710.4, 710.6 and 710.12 (third-party copies). General descriptions of spring and ball checks and of water hammer at a slamming valve are explanatory and uncited. No prices or lifespans.
Suggest a correction. We fix errors and say what changed.