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Entire irrigation zone lost pressure after filter cleaning
One sprinkler zone now has a weak, uneven spray pattern immediately after I cleaned the irrigation filter. Every head in that zone is affected, so I’m not planning to replace heads yet.
What’s the safest way to isolate the cause?
- A clogged or incorrectly reseated filter
- A partially closed isolation or zone valve
- A failing pressure regulator
- An underground leak on that zone
I can take static and running pressure readings before and after the backflow device and filter. Which readings would distinguish a restriction at the filter from a regulator or downstream leak? Also, should I check whether the valve solenoid and manual bleed screw are fully closed before digging?
There hasn’t been recent valve work or landscaping, but I’d also like to know whether unusually high water use would point more toward a buried leak than a pressure problem.
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4 replies
Compare pressure immediately before and after the filter with the zone running. A noticeable pressure drop across the filter under flow points to a clogged, damaged, or incorrectly seated filter. If pressure is already low before the filter, look upstream at the supply, backflow assembly, or regulator instead.
If pressure after the filter is normal with the zone off but drops sharply only when that zone runs, the restriction is more likely at the zone valve or downstream. Confirm the isolation valve is fully open, then check that the solenoid is snug and the manual bleed screw is fully closed. A loose solenoid or open bleed screw usually makes a valve stay partly or fully open when it should be off, but it is still worth ruling out before digging.
High water use can support the leak theory, especially if it continues when irrigation is not scheduled to run. But the running pressure comparison is the more useful first check: a large drop across the filter suggests the filter, while normal filter readings with poor zone pressure shifts attention to the valve or a downstream leak.
A static hold test can help before digging, provided the downstream piping can be isolated and pressurized for the test. With the zone off and no other irrigation or fixtures drawing water, watch the gauge for several minutes. Continued pressure decay supports a leak somewhere in that zone; stable pressure makes a leak less likely and shifts suspicion toward a restriction such as the zone valve, filter seating, or a partially closed isolation valve.
A small initial settling change after the valve closes can be normal, so look for continued decay rather than one brief movement. Also make sure no other open valve or connection is feeding the test side, or the reading will not isolate the zone.
The pressure-hold result isn’t conclusive unless the zone is truly isolated. If the zone valve isn’t sealing, supply pressure can keep feeding the downstream pipe, masking a buried leak or making the gauge behavior hard to interpret.
For a meaningful test, isolate the line downstream of the zone valve if there’s a separate shutoff, then pressurize and watch for continued decay. If there’s no downstream isolation point, a flow meter is more useful: with the zone off, any continuing flow indicates the valve may be passing water or the zone has a leak. A stable gauge by itself doesn’t reliably clear the buried line.
A flow-meter reading only helps if it isolates the suspect branch. If several zones share piping downstream of the meter, flow through another branch can appear to come from the suspect zone. Keep the other branches off or isolated before treating continuing flow as evidence of a passing valve or leak in that zone.