Code 90
Rinnai Abnormal Combustion / Combustion Performance Error

Unit displays Code 90; may be associated with poor combustion or sooting

Advertisements

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.

Advertisements

Possible Causes

Incorrect gas type or pressure, Blocked burner or vent, Improper air-fuel ratio, Faulty gas valve or fan speed control

How to Fix / Troubleshooting

Safety first: Turn OFF gas and power. Abnormal combustion can produce carbon monoxide; do not continue to operate the unit until corrected.

Steps to check:

  • Verify gas type: Confirm the unit is set up for the correct gas (NG or LP) and matches the supply.
  • Inspect burner and vent: Check for debris on the burner and ensure intake/exhaust vents are clear.
  • Check for visible soot: Soot around the exhaust terminal indicates poor combustion; stop using the unit.

When to call a professional: A licensed technician must perform combustion analysis, adjust gas pressure, and service or replace combustion components as needed.

Advertisements

Repair Difficulty

Professional Required 5/5

Required Part

Burner Assembly
Check Price on Amazon

We may earn a commission from links on this page.

Advertisements