AO3
Raypak
Combustion Air Temperature / Sensor Fault
Display shows 'AO3' and heater will not start; may be associated with intake air temperature or sensor fault.
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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
Failed intake air temperature sensor, Sensor wiring damage, Extremely high ambient air temperature, Faulty control board input
How to Fix / Troubleshooting
Safety first: Turn off power before accessing sensors.
Steps to address AO3 error:
- Locate air temperature sensor: On some high‑efficiency Raypak models, an air temp sensor is mounted near the combustion air intake or blower housing.
- Inspect sensor and wiring: Check for physical damage, corrosion, or loose connectors. Reseat the plug at the control board.
- Measure resistance: With power OFF, measure sensor resistance and compare to Raypak’s chart. Replace if out of range.
- Check ambient conditions: Ensure the heater is not installed in a confined, overheated space. Improve ventilation if necessary.
- Control board check: If sensor and wiring are good, the control board may be misreading the sensor and require replacement.
Note: Use only Raypak‑approved sensors to maintain correct calibration.
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Repair Difficulty
Medium
3/5
Required Part
Combustion Air Temperature Sensor
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