Noritz · Water heater
Code 31 Cold water inlet thermistor abnormality
What this code means
The sensor reading incoming (cold) water temperature isn't reporting a valid reading.
Most likely causes
- Failed or disconnected thermistor
- Corroded wiring connector at the sensor
What to try first
Not safely user-diagnosable beyond confirming stable power; needs a technician with the wiring diagram.
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 31 mean?
Cold water inlet thermistor abnormality. The sensor reading incoming (cold) water temperature isn't reporting a valid reading.
Can I fix Noritz code Code 31 myself?
Usually not. Not safely user-diagnosable beyond confirming stable power; needs a technician with the wiring diagram. If the code returns after one reset, it needs a licensed technician.
What causes Noritz code Code 31?
The most common causes are: failed or disconnected thermistor; corroded wiring connector at the sensor.
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.