Pressure Vacuum Breaker Backflow Preventer Troubleshooting
| Symptom | Probable Cause |
| Air inlet valve does not open as gauge drops to 0.0 psid. | Air inlet disc stuck to seat. |
| Air inlet valve does not open and differential on gauge will not drop. | Leaking No. 1 shut-off valve |
| Air inlet opens below 1.0 psid. | Dirty or damaged air inlet disc. |
| Scale buildup on disc or bonnet. | |
| Check valve opens below 1.0 psid. | Dirty or damaged check disc or seat o-ring. |
| Damaged seat. |
Click below for installation and maintenance sheets and freeze protection information:
720A
Installation, Maintenance, and Freeze Protection sheet
420 Installation,
Maintenance, and Freeze Protection sheet