AO / PS
Hayward
Pressure Switch Transition Fault
Heater shows AO or PS and shuts down when pump turns off; may chatter on/off at pump transitions.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Incorrect pump-heater interlock wiring, Pressure switch set too sensitive, Pump off delay not configured, Rapid flow changes from variable-speed pump
How to Fix / Troubleshooting
Safety First: Turn off power before adjusting wiring or switches.
- Verify pump interlock: Ensure the heater is wired to only receive a heat call when the pump is running, per Hayward wiring diagrams.
- Adjust pump programming: On variable-speed pumps, avoid very low RPMs when the heater is enabled. Program a minimum speed for heating.
- Check pressure switch: Some switches are adjustable. Follow the manual to set the switch so it closes reliably at normal flow but opens when the pump stops.
- Test operation: Run the system through on/off cycles and confirm the heater shuts down cleanly without error codes.
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Repair Difficulty
Medium
3/5
Required Part
Water Pressure Switch
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