Noritz · Water heater
Code 903 Combustion abnormality (sub-code)
What this code means
A more specific variant of the Code 90 combustion fault reported on some Noritz control boards.
Most likely causes
- Same underlying causes as Code 90: gas supply, pressure, or venting restriction
What to try first
Treat the same as Code 90 — check gas and venting, then call for professional gas-pressure testing.
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 903 mean?
Combustion abnormality (sub-code). A more specific variant of the Code 90 combustion fault reported on some Noritz control boards.
Can I fix Noritz code Code 903 myself?
Usually not. Treat the same as Code 90 — check gas and venting, then call for professional gas-pressure testing. If the code returns after one reset, it needs a licensed technician.
What causes Noritz code Code 903?
The most common causes are: same underlying causes as code 90: gas supply, pressure, or venting restriction.
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.