90
Noritz Abnormal Combustion / Gas Combustion Fault

Error code 90 appears; unit may shut down during operation.

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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, Wrong gas type, Dirty burner or heat exchanger, Blocked vent or intake, Improper air-fuel ratio

How to Fix / Troubleshooting

Safety first: Turn OFF power and gas. Do not continue to operate the unit with error 90; risk of unsafe combustion.

Steps to check and correct:

  • Verify gas type: Confirm the heater is configured for the correct gas (NG or LP) and that the supply matches.
  • Have gas pressure checked: A licensed technician should measure inlet and manifold pressure and adjust regulators as needed.
  • Inspect and clean burner: Remove burner and clean ports and surfaces of dust and debris. Reinstall correctly.
  • Descale heat exchanger: Perform a descaling flush to restore proper heat transfer.
  • Check venting and intake: Ensure vent and air intake are clear and installed per Noritz specifications.
  • Professional combustion tuning: A Noritz-trained technician should perform combustion analysis and adjust as required.
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Repair Difficulty

Professional Required 5/5

Required Part

Burner Assembly
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