Noritz · Water heater
Code 91 Incorrect gas type
What this code means
The unit is configured for a different gas type than what's actually supplying it (natural gas vs. propane).
Most likely causes
- Unit installed or converted without matching the gas type setting
- Conversion kit not installed correctly
What to try first
This is a setup/configuration issue that requires a licensed technician to correct safely.
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 91 mean?
Incorrect gas type. The unit is configured for a different gas type than what's actually supplying it (natural gas vs. propane).
Can I fix Noritz code Code 91 myself?
Usually not. This is a setup/configuration issue that requires a licensed technician to correct safely. If the code returns after one reset, it needs a licensed technician.
What causes Noritz code Code 91?
The most common causes are: unit installed or converted without matching the gas type setting; conversion kit not installed correctly.
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.