How to Winterize Your Sprinkler System And Backflow Preventer

Cold winter nights can be hard on your irrigation system. Water left inside sprinkler lines or an exposed backflow preventer can freeze, expand, and crack the equipment.

That’s why you must winterize your sprinkler system before a hard freeze. But do you need to blow out every sprinkler line? How do you drain a backflow preventer? And what should you do if you have never winterized the system before?

Here is how to prepare your irrigation system before the freezing weather arrives.

When Is The Perfect Time To Winterize a Sprinkler System?

There is no single date that works for every property. The best time for you to winterize is after your lawn no longer needs regular irrigation but before repeated overnight freezes begin.

You may need to pay extra attention if:

• Your backflow preventer is above ground.
• Parts of the irrigation system are exposed.
• Your property is in a colder or higher-elevation area.
• Your home will be vacant during winter.

If you are already preparing the rest of your outdoor plumbing, this is also a good time to winterize outdoor faucets and hose bibs.

How Should You Winterize Your Sprinkler System?

1. Shut Off the Irrigation Water Supply

• Find the valve that supplies water to your sprinkler system and shut it off. This is usually a separate irrigation shutoff, so you don’t normally need to turn off water to the entire house.
• Then put your sprinkler controller in Off or Rain Mode so it doesn’t try to run a watering cycle during winter.

If you are unsure which valve controls the irrigation system, avoid turning random valves until you know what they do. You can also refer to our guide on how to shut off the water supply to your home if you need help identifying the main shutoff.

2. Drain the Irrigation Lines

Now the remaining water needs somewhere to go. There are three common ways to drain an irrigation system, depending on the system you have.

Drainage	Advantage	Main Concern
Manual	Simple when correctly designed	Low areas may retain water
Automatic	Requires less hands-on draining	Does not mean every component is empty
Blowout	Clears water from difficult areas	Incorrect air pressure or airflow can damage the system

A manual or automatic drain may be enough if the system was designed to drain completely. But water can remain trapped in low spots, especially in systems with uneven pipe runs.

That’s where a sprinkler blowout may be needed.

3. Blow Out the Sprinkler Zones When Needed

Draining can remove much of the water from your sprinkler lines, but it may not get everything out. Water can remain trapped in low spots, valves, and sprinkler heads. When that water freezes, it can expand and damage the system.

That is where a sprinkler blowout can help. A professional uses a commercial air compressor to push the remaining water out through the sprinkler heads, usually one zone at a time.

But you should not connect just any compressor and turn up the pressure. A safe blowout depends on the right amount of airflow and pressure for your pipe material, pipe size, and system. Too much pressure can damage pipes, valves, fittings, or sprinkler components, while too little airflow may leave water behind.

Compressed air can also be dangerous. If you’re doing it yourself, wear eye protection, keep children and pets away, and never stand over a sprinkler head while air is moving through the system.

If you don’t know your system's safe pressure, pipe material, or correct connection point, it’s better to have an experienced professional handle the blowout.

How to Drain a Backflow Preventer for Winter?

A backflow preventer is a cross-connection control device that keeps irrigation water from flowing backward into your drinking water supply. Because many irrigation backflow assemblies are installed above ground, they are usually among the most exposed parts of the entire system.

A backflow preventer freeze can damage the body, internal components, test cocks, valves, or connected piping.

The exact procedure for draining a backflow preventer depends on the type of assembly and how it was installed.

• Isolate the main irrigation supply line.
• Relieve internal pressure by opening the appropriate test cocks and shutoff valves.
• Drain all residual water from internal chambers according to the manufacturer's guidelines.

Do not randomly loosen fittings or remove parts from an assembly you don't recognize. Backflow devices protect the potable water supply, so incorrect adjustments can affect more than your sprinkler system.

Once the assembly is properly drained, exposed piping and the backflow preventer may also need freeze protection. Insulation can help protect them from freezing temperatures, but it doesn’t replace proper draining.

What Are the Signs of a Frozen Backflow Valve?

Sometimes freeze damage becomes obvious during a cold spell. Other times, the problem doesn’t appear until you restart the irrigation system in spring.

Watch for:

• Cracks in the backflow body or fittings
• Water spraying or dripping from the assembly
• A damaged relief valve
• Split pipes near the device
• Water leaking when the irrigation supply is restored
• Unusual water pressure or sprinkler performance

If you discover a frozen backflow valve, do not immediately open the water supply and hope it works.

A small crack may leak heavily once full pressure returns. Have the assembly inspected first. Depending on the damage, individual components may be repairable, while a cracked or badly damaged assembly may need replacement.

For broader freeze protection around your property, see our guide on how to keep frozen pipes from bursting.

Which Winterization Mistakes Cause the Most Problems?

Winter damage does not always happen because a sprinkler system was completely ignored. It can also happen when only part of the system is winterized. Here are some common mistakes homeowners make:

• Assuming that shutting off the water is enough. It's not! Water already trapped downstream can still freeze.
• Draining the sprinkler zones but skipping the backflow preventer. Because the assembly is often above ground, it may be more exposed than the underground irrigation piping.
• Using compressed air incorrectly is another concern. More pressure doesn’t mean a better blowout. The system must stay within the limits of its components.
• Waiting too long until temperatures have already fallen well below freezing. If the backflow assembly is already frozen, operating valves or pressurizing the system can make existing damage worse.

What Should You Check Before Leaving the System for Winter?

Before considering the job finished, do a quick final check.

• Confirm that the irrigation water supply is off, the controller can’t accidentally start a watering cycle, and the required irrigation zones have been drained or blown out.
• Pay extra attention to anything above ground. Check the backflow preventer, exposed piping, valves, and hose connections.
• If something leaks, looks cracked, or will not shut off properly, repair it before winter rather than waiting until spring.
• Also be aware of what your homeowners policy covers before a winter plumbing emergency. To know more, you can read our guide on whether homeowners insurance may cover frozen pipes.

Frequently Asked Questions About Sprinkler and Backflow Winterization