Noritz · Water heater
Code 90 Combustion abnormality
What this code means
The fuel-air mixture during combustion is outside safe parameters, usually after repeated failed attempts to reach target temperature.
Most likely causes
- Gas supply or pressure issue
- Venting restriction affecting combustion air
What to try first
Check gas valve and vent clearance; this generally needs professional gas-pressure testing to resolve fully.
Safety note: if this code returns after one clean reset, stop resetting it — repeated lockouts usually mean a real fault that needs a licensed technician. Never bypass a safety switch.
FAQ
What does Noritz error code Code 90 mean?
Combustion abnormality. The fuel-air mixture during combustion is outside safe parameters, usually after repeated failed attempts to reach target temperature.
Can I fix Noritz code Code 90 myself?
Usually not. Check gas valve and vent clearance; this generally needs professional gas-pressure testing to resolve fully. If the code returns after one reset, it needs a licensed technician.
What causes Noritz code Code 90?
The most common causes are: gas supply or pressure issue; venting restriction affecting combustion air.
Other Noritz water heater codes
All Noritz water heater error codes →
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This information may contain errors or not apply to your exact model — always double-check it against your appliance's own manual before acting. If there's any chance of a gas, fire, electrical, carbon monoxide, or other safety hazard, stop and call a licensed professional or the appropriate agency (e.g. your gas utility) instead of relying on this page alone.