How To Dewinterize A Sprinkler System: The Complete Professional Startup Guide

Dewinterizing an irrigation system involves a systematic reintroduction of water pressure to the main and lateral lines to identify potential freeze damage while avoiding catastrophic "water hammer" events. By carefully managing the backflow preventer and sequencing zone activation, property owners can ensure peak hydraulic performance and prevent subsurface leaks from escalating into costly soil erosion or foundation issues.

Essential Planning and Equipment Checklist for Spring Startup

Before attempting to restore water flow to your irrigation network, you must ensure the environmental conditions are suitable. Reintroducing water while the ground is still frozen or during a period of overnight hard freezes can lead to immediate pipe rupture. Ideally, wait until the soil temperature consistently reaches 50°F (10°C) and the local frost forecast has cleared for at least ten consecutive days.

The dewinterization process, often referred to as "spring startup," typically requires 60 to 120 minutes depending on the number of zones and the complexity of the backflow prevention assembly.

Mandatory Equipment and Tools:

• Standard Irrigation Tools: A flathead screwdriver and a Phillips head screwdriver for adjusting spray heads and opening the controller cabinet.
• Valve Access: A long-handled T-handle water meter key or a specialized sprinkler valve key for deep-set curb stops.
• Pliers and Wrenches: Channel-lock pliers or a small pipe wrench for tightening loose fittings on the backflow preventer.
• Replacement Parts: A small supply of variable-arc nozzles, replacement filters, and at least one spare 4-inch pop-up spray head to address immediate failures.
• Documentation: Your original irrigation map or zone list to track performance and note necessary repairs.

Prerequisite Knowledge:

• Main Shut-Off Location: Usually located in the basement, crawlspace, or a dedicated utility pit near the water meter.
• Backflow Preventer Identification: You must know if your system utilizes a Pressure Vacuum Breaker (PVB), a Reduced Pressure Zone (RPZ) assembly, or a Double Check Valve (DCV), as the startup procedures for the test cocks vary slightly.

Phased Execution of the Irrigation Recommissioning Process

Success in dewinterizing a sprinkler system relies on incremental pressure increases. Moving too quickly can cause a surge of air and water that travels at high velocity, shattering plastic valves and fittings when it hits a dead end—a phenomenon known as hydraulic shock or water hammer.

Step 1: Environmental and Physical Site Inspection

Walk the entire property before touching any valves. Look for signs of "frost heave" where the ground has shifted, potentially exposing lateral lines or pushing sprinkler heads out of alignment. Inspect the backflow preventer assembly (usually the brass device located outside the home) for any visible cracks in the bell housing or brass body. If you see vertical fractures in the metal, do not proceed with the startup; the unit must be repaired or replaced first to prevent a major flood.

Step 2: Preparing the Backflow Preventer and Manual Drains

Most systems have manual drain valves located at low points in the piping to prevent freezing. Ensure all these manual drains are turned to the "closed" position (perpendicular to the pipe). On the backflow preventer, locate the test cocks—the small, nipple-like protrusions usually operated by a small flathead screwdriver. Turn the slots on these test cocks so they are perpendicular to the cock itself (closed).

Pro-Tip: If your backflow preventer was winterized correctly, the two large ball valve handles on the assembly should be at a 45-degree angle. Leave them in this position for now.

Step 3: Gradual Pressurization of the Main Line

This is the most critical stage of the process. Locate your main irrigation shut-off valve inside the house or in the meter pit.

1. Slowly turn the valve handle just a few degrees—enough to hear the faint hiss of water entering the line.
2. Wait for the sound of rushing water to diminish. This indicates the main line is filling and the air is being compressed.
3. Continue opening the valve in 25% increments, waiting 60 seconds between each turn.
4. Once the valve is fully open, return to the exterior backflow preventer.

Step 4: Activating the Backflow Assembly

With the main line pressurized up to the backflow device, you must now move water through the device and into the rest of the system.

1. Slowly turn the first ball valve (on the intake side) to the fully open position (parallel to the pipe).
2. Quickly flick the second ball valve (on the discharge side) to the open position. You may hear a loud "thunk" as the internal check valves seat themselves; this is normal.
3. If water continuously pours out of the air vent (the "bell" top) or the relief port, the internal springs or diaphragms may be stuck or damaged from the winter. Give the side of the unit a firm tap with the palm of your hand to help seat the components.

Warning: Never stand directly over the backflow preventer while opening the valves. If the unit has a catastrophic freeze crack that wasn't visible, the plastic canopy or internal components can become projectiles under 60-80 PSI of pressure.

Step 5: Sequential Zone Testing and Air Purging

Go to your irrigation controller (timer) and set it to "Manual Run" mode. You must test every zone individually, starting with the zone furthest from the water source to help purge trapped air effectively.

1. Activate Zone 1 and watch the heads pop up. Expect them to sputter and "spit" for the first 30-60 seconds as air is pushed out of the lines.
2. Once the flow is steady, check for "geysers"—heads where the plastic nozzle has blown off or the body has cracked.
3. Observe the base of each head for "bubbling," which indicates a cracked riser or a faulty wiper seal.
4. Check for "low pressure zones" where heads fail to pop up fully. This often signals a subsurface leak in the lateral line between heads.

Step 6: Micro-Adjustment and Nozzle Maintenance

While each zone is running, perform necessary maintenance to ensure the system meets its designed Precipitation Rate (PR).

1. Straighten Heads: If a head is leaning, it will cause uneven coverage. Hand-dig around the head and reset it so it is perfectly vertical.
2. Clean Filters: If a specific head has a weak radius, unscrew the nozzle and pull out the small plastic filter screen. Rinse it in a bucket of water to remove sediment that accumulated during the winter.
3. Adjust the Arc: Use your screwdriver to adjust the "left" and "right" stops on rotor heads to ensure you are watering the lawn, not the driveway or the side of the house.
4. Set the Controller: Once all zones are verified, program your spring schedule. In early spring, lawns typically require 30% to 50% less water than in July. Set the "Seasonal Adjust" or "Water Budget" feature on your controller to 50% to save water until the heat of summer arrives.

Technical Specifications for Irrigation System Components

To effectively dewinterize and maintain your system, you must understand the operating thresholds of your specific components. Using the wrong pressure or ignoring flow rates can lead to premature component failure.

Mitigating Subsurface Leaks and Mechanical Failures

Even a perfectly winterized system can suffer from the mechanical stresses of the freeze-thaw cycle. Identifying these issues early in the dewinterization process prevents high water bills and landscape damage.

• Scenario: The Backflow Preventer is Leaking from the Relief Port

  
  
  
  • Root Cause: Debris (sand or rust) from the main water line has lodged in the first check valve, or the internal rubber O-rings have dried out and cracked during the winter.
  • Actionable Fix: Turn off the water supply, disassemble the top of the backflow preventer, and rinse the internal check modules. Apply a thin layer of food-grade silicone lubricant to the O-rings and reassemble. If the leak persists, a "rebuild kit" for your specific model (e.g., Febco 765 or Wilkins 720A) is required.

• Scenario: Zone Fails to Activate from the Controller

  
  
  
  • Root Cause: The solenoid (the wire-connected cylinder on the valve) has failed, or the underground wiring has been damaged by rodents or soil movement.
  • Actionable Fix: Attempt to open the valve manually by turning the solenoid a quarter-turn counter-clockwise. If the zone turns on manually but not from the controller, the solenoid is likely burnt out and needs replacement. If it doesn't turn on manually, the internal diaphragm is likely stuck closed.

• Scenario: Drastic Pressure Drop Across All Heads in One Zone

  
  
  
  • Root Cause: A "Line Break." Typically caused by a large rock shifting against a PVC pipe during a freeze, creating a longitudinal crack.
  • Actionable Fix: Look for a "wet spot" or a patch of turf that is significantly greener or softer than the rest of the lawn. Dig down carefully to expose the pipe. Use a "telescoping repair coupling" (commonly called a Slip-Fix) to bridge the gap without needing to bend the pipe.

• Scenario: Sprinkler Heads "Misting" or Creating Fog

  
  
  
  • Root Cause: Excessively high water pressure (over 50 PSI at the head), which leads to water being blown away by the wind rather than soaking into the soil.
  • Actionable Fix: Install a pressure regulator at the valve or replace the standard spray heads with "Pressure Regulated" (PRS) heads, which are often mandated by modern building codes to ensure water efficiency.

Frequently Asked Questions

When is it safe to dewinterize my sprinkler system?

The safest time is after the "last average frost date" for your specific USDA Hardiness Zone. Generally, if you can dig a hole 6 inches deep and the soil is soft and moist rather than frozen or icy, the system is safe to charge.

Should I leave the air in the lines or blow it out?

The air must be purged during the startup process. As you turn on each zone, the water will push the air out through the sprinkler nozzles. This is why you should only run one zone at a time during startup; running multiple zones can trap air pockets that cause pipe-shaking vibration.

Why is my backflow preventer making a loud humming sound?

A humming or vibrating sound (resonance) usually indicates that the internal check valve is vibrating against its seat. This often happens if the water is turned on too slowly or if there is a slight pressure imbalance. Fully opening the ball valves quickly usually resolves the noise.

Do I need to have my backflow preventer tested every year?

In most jurisdictions, annual backflow testing by a certified professional is a legal requirement to ensure that irrigation water (which may contain fertilizers or animal waste) cannot be siphoned back into the city's clean drinking water supply.

Secure Your Landscape with a Professional Start

Proper dewinterization is the foundation of a healthy lawn and a low-maintenance summer. If you encounter significant leaks or feel uncomfortable managing high-pressure valves, contact a certified irrigation technician to perform a comprehensive system audit.