Noritz tankless water heater code Er31
Cold water thermistor open or short. Code Er31 means the same thing on all 2 Noritz series documented here — but the fix, and what it costs, is still worth reading for your exact unit.
What code Er31 means on each Noritz series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| NRCP | Cold water thermistor open or short | Part replacement | $120–$400 |
| NRCP Eco TOUGH | Cold water thermistor open or short | Part replacement | $120–$400 |
Each row opens the full page for that generation. We hold manuals for NRCP and NRCP Eco TOUGH, and each one gets its own reading of code Er31 — what Noritz documents, what you can safely check yourself, and what the repair should cost.
What each manual actually says
The table above compares 2 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 2 readings of code Er31 agree and where they part company.
NRCP — Cold water thermistor open or short
The cold water inlet sensor is open circuit or short circuit. Noritz groups four thermistor codes together in this table with one shared set of remedies: check the sensor and its connectors, check its resistance, and replace it if the resistance is open or short.
NRCP Eco TOUGH — Cold water thermistor open or short
The cold water inlet sensor is open or short circuit. Noritz groups four sensor codes with one set of remedies on this generation: check the temperature sensor and that connections are secure, check the sensor resistance and replace it if the resistance is zero, and contact technical support. Auto reset.
Does it matter which Noritz you have?
NRCP and NRCP Eco TOUGH all route code Er31 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.
Which Noritz do you have?
On the 2 series that report code Er31, the model number on the rating label starts NRCP — match yours against the 4 listed below. You can also use the full model-number decoder.
Where this comes from
Source: Noritz Service Manual — NRCP111-DV / NRCP98-DV (Rev. 09/19) (p. 62), read Sep 2026 — the manufacturer's own documentation for this Noritz range.
Source: Noritz Service Manual — NRCP1112-DV / NRCP982-DV Eco TOUGH (Rev. 05/19) (p. 58), read Sep 2026 — the manufacturer's own documentation for this Noritz range.
Parts, guides and symptoms behind code Er31
Code Er31 on these 2 Noritz series points at 1 part and 2 symptoms, each named by the manufacturer's own procedure for this code.