90
Rinnai
Abnormal Combustion or Gas Combustion Fault
Boiler locks out with error 90; may occur during high fire or under heavy load.
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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 gas pressure, Blocked burner or heat exchanger, Improper venting causing recirculation, Incorrect gas type setting
How to Fix / Troubleshooting
Safety first: Turn off power and gas. Do not continue to operate the boiler with an abnormal combustion fault.
- Check venting and air supply: Inspect intake and exhaust terminations for blockages and verify correct installation per Rinnai guidelines.
- Confirm gas type and settings: Ensure the boiler is configured for the correct gas type and that any conversion kits have been properly installed.
- Visual burner inspection: After cooling, remove the burner cover and inspect for heavy soot, rust, or debris. Do not attempt to adjust burner ports without training.
- Professional combustion analysis: A qualified technician must perform a combustion test with a flue gas analyzer and adjust gas valve settings or replace components as needed.
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Repair Difficulty
Professional Required
5/5
Required Part
Burner Assembly
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