Common symptoms include persistent leaking or spraying, water continuing to flow when it should stop, weak or irregular downstream flow, and chattering, humming or vibration. These signs can indicate a fault, but none proves the anti-siphon valve itself has failed.
Signs of a likely fault
- Persistent leaking or spraying: Continuous water from the atmospheric vent, valve body or connections is abnormal. Mineral deposits, corrosion or staining may reveal an intermittent leak.
- Water not shutting off: Continued flow may indicate a problem if the anti-siphon device is combined with a control valve. On other designs, the separate tap, solenoid or shut-off component may be responsible.
- Weak, pulsing or irregular flow: A restricted or unstable valve can affect downstream flow, although supply, pressure and control faults can cause similar symptoms.
- Unusual noise or vibration: Chattering, humming, whistling or vibration may indicate unstable operation, but noise alone does not confirm valve failure.
- Possible loss of backflow protection: Suspected reverse flow or an unexplained change in water quality requires prompt assessment. Do not deliberately create reverse flow to test the valve.
Normal discharge or a fault?
Some anti-siphon designs briefly release water during shut-off or a pressure change; others should not. Check the manufacturer’s instructions where available. Discharge is more likely faulty when it is continuous, forceful, occurs while the system is idle, or accompanies poor flow or failure to stop.
Note when the problem occurs, how long it lasts and which outlet or irrigation zone is operating. These are safe observations only.
Do not cap the vent, dismantle the valve or attempt a backflow test. This could defeat its protection or expose you to pressurised or contaminated water. If safe, stop using the affected connection. For persistent leaks, unreliable operation or suspected contamination, contact our Sydney plumbing team for assessment by a licensed plumber.