Takagi Non-Condensing Code 331
Mixing thermistor fault (T-D2). The sensor on the mixing side is not reporting correctly. Takagi lists this code with a three-digit display only — it is marked N/A for the T-K4 and T-KJr2, which do not report it.
Part replacementThe verdict
Replace a part
A sensor rather than the valve it watches, which keeps it at the cheaper end. Expect the outlet temperature to be less stable until it is replaced.
Typical cost: $150–$450
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 Non-Condensing — not averaged across the brand.
Source: Takagi Non-Condensing Models On-Demand Water Heater Troubleshooting Guide (p. 12), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Note whether the temperature swings during a shower.
- Book a service call.
Frequently asked questions
My T-K4 will not show this code?
Correct. Takagi's table marks 331 as N/A for both the T-KJr2 and the T-K4 — there is no two-digit or flash equivalent. It is a T-D2 code on this range.
Code 331 on other Takagi 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
2 other Takagi Non-Condensing 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: