Noritz EZ Series & NCC199CDV Code 31
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.
Also displayed as: F31
Part replacementThe verdict
Replace a part
Cheap part and a short visit. Worth fixing rather than living with, because a wrong inlet reading makes the appliance mis-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 EZ Series & NCC199CDV — not averaged across the brand.
Source: Noritz Service Manual — NRC663 FSV, EZ98DV, EZ111DV, NCC199CDV (Rev. Oct 2017) (p. 32), read Sep 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- 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
5 other Noritz EZ Series & NCC199CDV 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: