Leaking Backflow Preventer: Common Causes and What to Do

A leaking backflow preventer is one of the more common sprinkler calls in North Texas, especially after cold weather. The leak may be a slow drip, a steady trickle or a spray. Some leaks affect only the irrigation system; all of them waste water. This article explains the common causes, what you can check and what should be left to licensed professionals.

First: Shut It Down if Needed

If the assembly is spraying or leaking heavily, close the irrigation isolation valve upstream of it. This valve is usually between the water meter and the backflow preventer. If there is no separate isolation valve, close the shutoff valve on the inlet side of the assembly. Fort Worth’s irrigation code calls for an isolation valve between the meter and the backflow preventer, so most newer systems have one.

Where the Leak Is Coming From

Look closely to see where the water is leaving the assembly. The location points to the cause.

From a test cock

The small test cocks on the side of the assembly can leak if they are loose, damaged or were left partly open after a test. A small leak here is often a simple fix for a technician.

From a shutoff valve handle

The handles on the shutoff valves have packing or seals around the stem. These can wear and weep water, especially when the valve is turned after sitting for a long time.

From the body or a cover

Water coming from the body itself, a seam, or around a bonnet or cover can mean a cracked casting, a worn gasket or loose bolts. A crack is common after a freeze.

From a relief valve or vent

Some assembly types, such as reduced pressure zone assemblies, have a relief valve that discharges water when internal pressures are out of balance. A discharge here is the assembly doing its job, but it means something inside needs attention, often debris on a check valve or a worn seal.

From the fittings

Leaks where the assembly connects to the pipe can come from loose unions, cracked fittings or freeze damage to the pipe right next to the assembly.

Common Causes

• Freeze damage. Water trapped in the assembly expands when it freezes and can crack the body or internal parts. This is the most common cause after a cold snap. Our guide to protecting your backflow preventer from freezing explains how to prevent it.
• Debris. Sand, grit or pipe shavings, especially after a water main repair, can lodge on a check valve seat and keep it from sealing.
• Worn rubber parts. Seals, discs and O-rings wear with age.
• Pressure changes. Surges from valves closing can stress seals.
• Physical damage. Mowers, trimmers and vehicles can hit exposed assemblies.

What You Can Do

• Shut off water to the irrigation system if the leak is heavy.
• Take photos of where the leak is coming from.
• Check that test cocks are closed; they should be turned so the slot is perpendicular to the flow, but do not force them.
• Keep the area around the assembly clear so a technician can reach it.

What You Should Not Do

• Do not take the assembly apart.
• Do not replace it with a different part or a plain pipe.
• Do not remove it to “fix” the leak and run the system without it.

In Fort Worth, any irrigation system connected to the public water supply must have an approved backflow prevention assembly. Replacements and relocations require a plumbing backflow permit, and repairs must be followed by a test from a registered Backflow Prevention Assembly Tester. Our article on backflow testing in Fort Worth explains the process.

Repair or Replace?

Many leaks can be fixed by cleaning the check valves and replacing rubber parts with a manufacturer’s repair kit. Replacement is usually the better choice when:

• The body is cracked
• Parts are not available for the model
• The assembly has failed repeatedly
• The assembly is not on the city’s approved list

Either way, the assembly must be tested after the work.

Leaks That Show Up in Spring

If the system sat through a cold winter, the first time it is turned on in spring is when many backflow leaks appear. Open the valves slowly and watch the assembly for a minute or two before running zones. Our guide on turning your system back on in spring walks through a safe startup.

Why It Matters

A leaking backflow preventer wastes water every minute it is pressurized, since it sits on the supply side of the zone valves. It can also cause low pressure throughout the system. More important, a damaged assembly may not protect the drinking water supply the way it should.

Keeping Water Away From the Foundation

Many assemblies sit right next to the house. A leak that runs for days keeps the soil at that corner of the foundation much wetter than the rest. On expansive clay, uneven moisture around a foundation is something to avoid. If you find the soil around the assembly soaked, shut off the irrigation water until the leak is fixed and let the area dry. If water from the assembly or from roof runoff tends to collect against the house there, our drainage service can look at grading and drainage options.

When to Call a Technician

Any leak from the body, relief valve or internal parts of the assembly is a job for a licensed professional. Our sprinkler repair team can help arrange repair or replacement and the required test. For background on what the assembly does, see our backflow preventer guide. For leaks elsewhere in the system, see our article on signs of a hidden sprinkler leak.