I have a lf009mq2t watts backflow preventer which starts spewing water from its center nozzle anytime any of my three irrigation lines stops running (or if I run a hose while its valve is off). I can make it stop spewing by running any water in the house for a few seconds until what looks like some white air is pushed out. It used to work perfectly for four years since installation. What can I do?

backflow preventer label

the location on the preventer where the water leaks

A video of water flowing in the kitchen sink to stop the spewing water. (Also, full size images.)

  • Your backflow preventer is a Reduced Pressure Principle (RPP) (sometimes called RPZ for Reduced Pressure Zone) unit, and these are required to be tested by a plumber or other qualified serviceperson on a periodic basis -- have you tried contacting whoever does the tests on it for service? Commented Sep 30, 2021 at 3:27
  • Also, I take it the backflow preventer spews continuously until you run water in the house, and the house water is tapped off upstream of the backflow preventer? Commented Sep 30, 2021 at 3:32

1 Answer 1


Your RPZ needs servicing

That sort of continuous spitting or streaming from a Reduced Pressure Principle/Zone (RPP or RPZ) assembly with nothing going on downstream is a sign that the assembly needs to be serviced. In particular, Watts' own troubleshooting guidance video on the topic says that if the relief port is spitting, dripping, or streaming continuously in a no-downstream-flow condition, one should close the downstream valve on the assembly, then open the most-downstream (#4) test cock with a standard screwdriver to relieve pressure on the chamber. If the flow from the relief valve drain stops, then that's a sign the first check is fouled or sticking; if it continues, then the relief valve itself is not seating.

Either way, you'll need to either get a rebuild kit and service the RPZ yourself with it following the instructions in the video or installation manual, or have a plumber or irrigation technician qualified as a backflow preventer tester fix it for you. Some local codes may require that a qualified tester perform the repair, even, and will also require in that case that the unit be tested regularly by said qualified tester.

P.S. if you haven't a clue about finding someone who's qualified to work on backflow assemblies and don't feel comfortable DIYing this, call your water utility! They'll be able to get you a list of referrals at minimum, and may even be willing to send a technician out to test it themselves, depending on utility policies.

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