What a check valve does and why your pump needs one
A check valve is a one-way gate that lets water flow up from your well into your pressure tank, but stops it from flowing backward when the pump shuts off. Without one, water in the discharge line drains back down into the well every time the pump stops. This means your pump has to refill that line every time it starts again — wasting energy and wearing out the pump faster.
Check valves are typically installed on the discharge side of the pump, between the pump outlet and the pressure tank. They cost between $15 and $50 depending on the size and type, and the job takes an hour or two if you have basic plumbing tools.
Key Takeaways
- A check valve prevents water from flowing backward into your well when the pump stops, reducing wear and energy waste.
- You will need to turn off power to the pump, drain the discharge line, and unscrew the fitting where the valve installs.
- The valve body has an arrow showing the direction water should flow — this arrow must point toward the pressure tank, not the well.
- After installation, you will need to bleed air from the discharge line before restarting the pump.
- If your pump already has a check valve and it is failing, you may see the pump cycling on and off more often than usual.
Tools and materials you will need
Gather these items before you start. You will need an adjustable wrench or two pipe wrenches (one to hold the fitting steady, one to turn the nut), a bucket or pan to catch water, a check valve sized to match your discharge line (usually 1 inch or 1.25 inches), and plumber's tape (also called PTFE tape or Teflon tape) to seal the threads.
If your discharge line is connected with unions (two-part fittings that screw together), you can unscrew those without cutting the pipe. If it is soldered copper or glued PVC, you will need a hacksaw or PVC cutter to cut the line and a coupling to reconnect it after the valve is in. Have a bucket ready — there will be water in the line.
Shutting down the pump and draining the line
Turn off the circuit breaker that powers the pump. Do not skip this step — you do not want the pump to start while you are working on it. Wait a few minutes for any residual pressure to drop.
Open the drain valve at the lowest point of the discharge line (usually near the pump or at the base of the pressure tank). Let the water drain into a bucket until it stops flowing. If there is no drain valve, you will lose some water when you open the fitting, so have your bucket ready. Once the line is empty, you can safely disconnect the fitting.
Removing the old fitting and preparing the connection
Use one wrench to hold the fitting body steady while you turn the nut with the second wrench. Turn counterclockwise. If the fitting is stuck, explore penetrating oil and wait 10 minutes before trying again. Once the nut is loose, you can usually unscrew it by hand.
If the line is soldered or glued, cut it with a hacksaw or PVC cutter about 6 inches from the pump outlet. You will install the check valve in this gap and use a coupling to rejoin the line on the other side. Clean any burrs from the cut end with a file or sandpaper.
Installing the check valve with the flow direction correct
Look at the body of the check valve. It will have an arrow stamped or printed on it. This arrow shows the direction water must flow through the valve. The arrow must point away from the pump, toward the pressure tank. If you install it backward, water will not flow at all and the pump will not build pressure.
Wrap the male threads (the part that screws in) with plumber's tape. Wrap it clockwise three times around the threads — this seals the connection and prevents leaks. Screw the valve onto the pump outlet by hand first, then tighten it with a wrench. Do not overtighten; snug is enough. If you are using a coupling on the other side (because you cut the line), wrap and install that the same way.
Reconnecting the discharge line and bleeding air
Once the check valve is installed, reconnect the discharge line to the outlet side of the valve. If you cut the line, use a coupling and wrap both ends with plumber's tape before screwing them in. If you have a union, screw it back together hand-tight, then snug it with a wrench.
Before you turn the pump back on, you need to bleed air from the discharge line. Open the drain valve again and turn the pump back on. Water will flow out of the drain for a few seconds, then air will come out as bubbles. Once water flows steadily without bubbles, close the drain valve. This removes the air pocket that would otherwise cause the pump to cycle or lose pressure.
Testing the pump and checking for leaks
Turn the pump on and let it run until the pressure tank reaches its normal operating pressure (usually 40 to 60 pounds per square inch, shown on the pressure gauge). Watch the discharge line and all the connections you just made for drips or sprays. A small weep at a threaded connection usually stops once the water pressure stabilizes, but a steady drip means the connection is not tight enough.
If you see a leak, turn off the pump, drain the line again, and tighten the fitting a quarter turn with a wrench. Refill and test again. Do not over-tighten — you can crack the valve body or strip the threads.
Frequently Asked Questions
Can I install a check valve on an existing well pump that does not have one?
Yes. You will cut or unscrew the discharge line between the pump and the pressure tank, install the valve with the flow arrow pointing toward the tank, and reconnect the line. The job is the same whether you are replacing a failed valve or adding one for the first time.
What size check valve do I need?
The valve must match the diameter of your discharge line. Most residential well pumps use 1-inch or 1.25-inch lines. Look at the fitting where the line connects to the pump or tank, or measure the outside diameter of the pipe itself. Take that measurement to a plumbing supply store and they will give you the right size.
How do I know if my check valve is failing?
A failing check valve usually causes the pump to cycle on and off more often than normal, even when no water is being used. You may also hear a loud thud or bang when the pump shuts off — this is water slamming backward against the valve. If the valve is stuck open, water will drain back into the well and the pump will run longer to refill the tank.
Do I need to turn off the power before installing a check valve?
Yes. Always turn off the circuit breaker before you work on any part of the pump or discharge line. This prevents the pump from starting unexpectedly while you are loosening fittings or working near moving parts.
What if water leaks from the threads after I install the valve?
A small drip usually stops once the system pressurizes. If it continues, turn off the pump, drain the line, and tighten the leaking fitting one quarter turn with a wrench. Refill and test. If it still leaks, you may need to remove the fitting, add more plumber's tape, and reinstall it.