Quick Answer:
When an irrigation zone shuts off quickly it can send a pressure wave back into your house plumbing. That transient spike—sometimes brief but strong—can stress pipes, fittings, fixtures and appliances. Start by installing a pressure gauge at a convenient point, isolate the pressure regulator or backflow assembly to see if the spike originates there, and monitor the timing of the surge versus irrigation shutdowns to identify the source.
Why This Happens
Water moving at speed has momentum. When a valve in an irrigation line closes suddenly, that momentum is converted into a pressure wave that travels back through the system. In a residential plumbing network this shows up as a short, high-pressure pulse—often called a transient or water hammer. Backflow preventers and pressure reducing valves (PRVs) can change flow patterns or cycle as irrigation ends, which can either generate or amplify the spike. In some cases the transient is strong enough to cause leaks, damage seals, or make nearby taps act unpredictably—like when Water sprays violently when tap opens or when you notice Pressure increases after backflow device cycles.
Step-by-Step What to Do
Step 1 — Install a pressure gauge
- Fit a reliable pressure gauge at an accessible point on the incoming cold-water line (near the main shutoff or after the PRV). A simple test gauge will show if spikes occur and how large they are.
- Record normal static pressure, then watch the gauge while an irrigation zone shuts off to capture the transient. Take notes of peak values and duration.
Step 2 — Isolate the PRV and backflow device
- Close the isolation valves that let you separate the domestic plumbing from the irrigation system and any PRV or backflow assembly. Doing this lets you see whether the pressure spike originates upstream or downstream of those devices.
- If the spike disappears with the irrigation side isolated, the problem is in the irrigation piping or the backflow/PRV area. If it persists, it may be in the house plumbing.
- Do not disassemble a backflow preventer unless you are certified to test or repair it; many jurisdictions require licensed technicians for backflow devices.
Step 3 — Monitor surge timing
- Log the exact moment an irrigation valve closes and the moment the pressure spike appears on your gauge. Note delays of a few seconds versus immediate spikes—this helps pinpoint the location and mechanism.
- Repeat the test on different zones and at different times. Some valves or controllers age and behave differently under certain pressures or temperatures.
Step 4 — Small, safe fixes to try
- Check that irrigation valves close cleanly and that solenoids are not oscillating or failing to seat. Replace or rebuild valves that hammer when they shut.
- Where appropriate, add slow-closing valves or modify valve closing speed on the irrigation controller to reduce sudden stoppage of flow.
- Consider installing properly sized arrestors or surge dampeners on the domestic side if tests show transients entering the house plumbing. If you do this yourself, use products rated for potable water systems and follow manufacturer instructions.
What Not to Do
- Do not ignore surges—they cause fixture and appliance failure.
- Do not remove or tamper with a backflow preventer if you are not qualified; those devices are critical for water safety and often legally regulated.
- Do not assume the irrigation controller is harmless—faulty wiring or failing solenoids can cause rapid valve cycling and repeated surges.
When to Call a Professional
- If pressure spikes exceed safe limits on your gauge (for example, transient peaks well above your normal maximum working pressure).
- If you suspect a failing backflow preventer or PRV—these often require a certified tester or licensed plumber to inspect and repair.
- If you find leaks, persistent noise, or repeated appliance failures that you cannot trace and fix with basic valve checks and timing tests.
Safety Notes
- Turn off and depressurize lines before working on fittings or valves. Open a tap after closing the main to relieve pressure before loosening connections.
- Follow local codes for backflow device work; improper handling can contaminate the potable supply and carry legal penalties.
- When in doubt about electrical components on irrigation valves or controllers, shut off power before inspecting wiring and call an electrician if you are unsure.
Common Homeowner Questions
- Why does my gauge show only brief spikes? Short spikes are typical for transients; the duration is brief but the peak can be damaging if high enough.
- Will a surge protector for water plumbing stop this? Properly sized water hammer arrestors or surge dampeners can reduce spikes, but they must be installed in the right location and sized for the system.
- Can I test this safely myself? Yes—install a gauge, isolate irrigation, and time events—but avoid tampering with backflow devices or high-pressure fittings if you are not trained.