Noritz NRC Series Code 31
Cold water thermistor fault. The sensor reading the incoming cold water temperature is out of range. Noritz checks its resistance and its connection, with the two display-window codes separating an open circuit from a short. The unit needs this reading to work out how much heat to add, so a bad one shows up as temperature that will not settle.
Also displayed as: 311, 312
Part replacementThe verdict
Replace a part
Inexpensive part, quick replacement, inside the cabinet. Worth doing rather than living with: a wrong inlet reading makes the unit over- or under-fire on every draw.
Typical cost: $120–$400
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the NRC Series — not averaged across the brand.
Source: Noritz Service Manual — NR501-OD, NR662-OD, NRC661, NRC711 (Rev. Dec 2013) (p. 28), read Sep 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Note the display-window code — 311 is an open circuit, 312 a short.
- Book a service call.
Code 31 on other Noritz series
The same code number can mean something different on another series — make sure you're reading the page for your exact unit:
Don't confuse this with
4 other Noritz NRC Series codes point at a thermistor too. They are different components in different places, and ordering a part against the wrong one is the most common way this fault gets expensive: