Takagi tankless water heater code 331
Your series decides which reading applies. Across the 2 Takagi series documented here, code 331 is listed as mixing thermistor fault (1 series) and mixing thermistor fault (t-d2) (1 series). Find your series in the table below, where those readings route to a replacement part.
What code 331 means on each Takagi series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| Condensing | Mixing thermistor fault | Part replacement | $150–$450 |
| Non-Condensing | Mixing thermistor fault (T-D2) | Part replacement | $150–$450 |
Each row opens the full page for that generation. We hold manuals for Condensing and Non-Condensing, and each one gets its own reading of code 331 — what Takagi 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 Takagi wording behind each row, one entry per manual, so you can see where the 2 readings of code 331 agree and where they part company.
Condensing — Mixing thermistor fault
The sensor on the mixing side — where heated water is blended with bypassed water to hold the outlet temperature — is not reporting correctly.
Non-Condensing — 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.
Does it matter which Takagi you have?
Condensing and Non-Condensing all route code 331 the same way: a replacement part, at $150–$450. That makes it one of the Takagi 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 Takagi series that reports code 331, so they are safe to work through before you have identified your exact unit. They also cost nothing.
- Note whether the temperature swings during a shower.
- Book a service call.
That is 2 of the 2 checks documented for code 331. The rest differ by generation, so if none of those explains it, go to your own series above.
Which Takagi do you have?
On the 2 series that report code 331, the model number on the rating label starts T — match yours against the 3 listed below. You can also use the full model-number decoder.
Where this comes from
Source: Takagi Condensing Models On-Demand Water Heater Troubleshooting Guide (p. 13), read Aug 2026 — the manufacturer's own documentation for this Takagi range.
Source: Takagi Non-Condensing Models On-Demand Water Heater Troubleshooting Guide (p. 12), read Aug 2026 — the manufacturer's own documentation for this Takagi range.
Parts, guides and symptoms behind code 331
Code 331 on these 2 Takagi series points at 2 parts and 1 symptom, each named by the manufacturer's own procedure for this code.