Noritz tankless water heater code 31
Your series decides which reading applies. Across the 5 Noritz series documented here, code 31 is listed as inlet thermistor fault (3 series) and cold water thermistor fault (2 series). Find your series in the table below, where those readings route to a replacement part.
What code 31 means on each Noritz series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| EZ Series & NCC199CDV | Cold water thermistor fault | Part replacement | $120–$400 |
| NCC199 & NRC111 | Inlet thermistor fault | Part replacement | $120–$400 |
| NR50, NR66 & NR71 | Inlet thermistor fault | Part replacement | $120–$400 |
| NR98 & NR111 | Inlet thermistor fault | Part replacement | $120–$400 |
| NRC Series | Cold water thermistor fault | Part replacement | $120–$400 |
Each row opens the full page for that generation. We hold manuals for EZ Series & NCC199CDV, NCC199 & NRC111, NR50, NR66 & NR71, NR98 & NR111 and NRC Series, and each one gets its own reading of code 31 — what Noritz documents, what you can safely check yourself, and what the repair should cost.
What each manual actually says
The table above compares 5 series in four columns, which is enough to route you and not enough to explain anything. This is the Noritz wording behind each row, one entry per manual, so you can see where the 5 readings of code 31 agree and where they part company.
EZ Series & NCC199CDV — Cold water thermistor fault
The incoming cold water sensor is out of range. Noritz measures its resistance, checks for an open or short circuit, and checks the connection. The unit uses this reading to work out how much heat to add, so a bad one shows up as temperature that will not settle.
NCC199 & NRC111 — Inlet thermistor fault
The incoming water sensor is out of range. Noritz measures its resistance, checks for an open or short circuit, and checks the connection. The unit needs this reading to decide how much heat to add.
NR50, NR66 & NR71 — Inlet thermistor fault
The incoming water sensor is out of range. Noritz measures its resistance and checks for an open or short circuit and an improper connection. Three flashes on an NR71 or N-0631S with no remote controller, and Noritz notes against that row that the unit will not simply work after a reset if the minimum flow rate is available immediately.
NR98 & NR111 — Inlet thermistor fault
The incoming water sensor is out of range. Noritz measures its resistance, checks for an open or short circuit, and checks the connection. The unit needs this reading to decide how much heat to add. This range covers seventeen model numbers, from the residential NR98 to the commercial NC380-SV-ASME, and the inlet sensor is the same part across all of them — one of the few components on this table that does not vary with the model.
NRC Series — 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.
Does it matter which Noritz you have?
EZ Series & NCC199CDV, NCC199 & NRC111, NR50, NR66 & NR71, NR98 & NR111 and NRC Series all route code 31 the same way: a replacement part, at $120–$400. That makes it one of the Noritz numbers you can act on before working out which unit you own.
What to check first, whatever your series
These checks are on the manufacturer's list for every Noritz series that reports code 31, so they are safe to work through before you have identified your exact unit. They also cost nothing.
- Book a service call.
That is 1 of the 2 checks documented for code 31. The rest differ by generation, so if none of those explains it, go to your own series above.
Which Noritz do you have?
On the 5 series that report code 31, the model number on the rating label starts EZ, NCC, GQ, N and NRC — match yours against the 43 listed below. You can also use the full model-number decoder.
Where this comes from
Source: Noritz Service Manual — NRC663 FSV, EZ98DV, EZ111DV, NCC199CDV (Rev. Oct 2017) (p. 32), read Sep 2026 — the manufacturer's own documentation for this Noritz range.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 55), read Sep 2026 — the manufacturer's own documentation for this Noritz range.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 54), read Sep 2026 — the manufacturer's own documentation for this Noritz range.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 56), read Sep 2026 — the manufacturer's own documentation for this Noritz range.
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 Noritz range.
The same number on other brands
Code 31 is not a standard across the industry — every manufacturer publishes its own table. If your unit is not a Noritz, this number means something else entirely:
Parts, guides and symptoms behind code 31
Code 31 on these 5 Noritz series points at 1 part and 2 symptoms, each named by the manufacturer's own procedure for this code.