Leaking Backflow Preventer? A Step-by-Step Guide to What to Do
A leaking backflow preventer is not usually an emergency, but it is always a message. Where the water is coming from tells you a lot about what is wrong, and the answer changes what you should do next.
Before anything else: a backflow assembly is a legally regulated device. Once it has been opened up or had parts replaced, it has to be re-tested and the passing report filed with your water purveyor before the property is back in compliance. That single fact is why most of the DIY advice you will find on this topic is a bad idea. This page walks through diagnosis honestly, then tells you where the line is.
Step one: find out where the water is actually coming from
Stand where you can see the whole assembly and identify the exact source. There are only a handful of possibilities, and they mean very different things.
Water coming out of the relief valve on the bottom
If you have a reduced pressure assembly (RP, sometimes called RPZ), the port on the underside is the relief valve. It is supposed to discharge. That is its entire job.
A brief spit during a pressure swing, when a pump kicks on or a fire hydrant gets used nearby, is the device doing what it was designed to do. A steady stream that does not stop is different. That usually means the first check valve is fouled with debris and no longer holding the required pressure differential, or the relief valve seat itself has debris on it. Common after a water main break, when the system fills with grit.
Water at a union, flange, or the seam of the body
This is a seal or a casting problem rather than a check valve problem. In Southern California the usual cause is age, though we do see freeze cracks after cold snaps in the high desert and inland valleys. A cracked body is a replacement, not a repair.
Water at a test cock
The four small valves on the side are test cocks. If one is weeping, it was often left slightly open after a test or has a worn seat. Minor, but it still needs to be corrected.
Water at a shutoff valve stem
The gate or ball valves on either end are technically part of the assembly, and a packing leak there is a different repair than anything inside the device.
Step two: decide whether it needs to be shut off
Most leaks do not require you to close anything. If the discharge is significant enough to flood a vault, undermine a walkway, or run into a building, close the downstream shutoff first, then the upstream one.
Two warnings. If the assembly protects a fire line, do not close anything without notifying your fire protection contractor and, in most cities, the fire department. Shutting a fire service without authorization is its own serious problem. And do not ever remove the assembly and connect the pipe straight through to stop a leak. That is an open cross-connection, and it is the thing every one of these rules exists to prevent.
Photograph it before you do anything. A picture of where the water is coming from and how fast tells a tester more in five seconds than a phone call does in five minutes, and it often determines what parts get loaded on the truck.
Step three: understand what you can and cannot do yourself
You can close a test cock that was left open. You can clear debris away from the assembly, pump out a flooded vault, and remove a lock so someone can get to it.
What you should not do is open the device. Replacing checks, seats, springs, rubber or the relief valve assembly is repair work on a certified assembly. In California, testing has to be performed by a certified tester, and the report has to reach your purveyor. If an uncertified repair is made and never re-tested, the property is out of compliance whether or not the leak stopped, and you will not find that out until a notice arrives.
There is also a practical reason. Repair kits are brand and model specific. A Febco, a Watts, a Wilkins and a Conbraco of the same size do not share parts. Guessing usually means two trips instead of one.
Step four: get it repaired and re-certified together
The repair and the re-test belong in the same visit. That is the part people miss. A plumber can absolutely stop the leak, but if that plumber is not a certified backflow tester, you now need a second company to come out, test it, and file the report before the property is compliant again.
We carry repair parts for every major brand on the trucks for exactly this reason, so most repairs happen on the same visit as the diagnosis, and the re-certification is included when we do the repair ourselves.
How to keep it from happening again
Most of what shortens an assembly's life in Southern California is environmental rather than mechanical. Debris after main work is the biggest single cause of fouled checks. Standing water in a below-grade vault corrodes everything and makes every visit harder and more expensive. Direct sun degrades rubber over years. And devices that sit in enclosures nobody opens between annual tests tend to hide problems until the test finds them.
The annual test is the real preventive maintenance here. It is the one time a year somebody puts a gauge on the device and finds out what is actually happening inside it.
Common questions
Is a dripping relief valve always a failure?
No. Intermittent discharge during pressure fluctuation is normal behavior for an RP. Continuous discharge is not, and should be looked at.
Can I just plug the relief valve to stop the water?
No, and please do not. Plugging the relief valve defeats the protection the device exists to provide and turns a leak into a live contamination risk.
Does a repair reset my annual due date?
That depends entirely on your purveyor. Some treat a passing repair test as the new annual test, others keep you on a fixed compliance month regardless. It is worth asking rather than assuming, because the two rules produce very different due dates.
How fast can someone get out there?
For an active leak, usually same or next day. Call the office at (562) 343-1436 and describe where the water is coming from.