Takagi Non-Condensing Code 311
Output thermistor fault. The sensor reading the temperature of water leaving the heater is not reporting correctly. Shown as 31 on a T-K4 or T-KJr2 remote, or two flashes of the red LED.
Also displayed as: 31
Part replacementThe verdict
Replace a part
A cheap sensor with a service call around it. Until it is replaced the unit is holding temperature without its most important reading.
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 how the temperature behaves at the tap.
- Note when the unit was last flushed — scale on a water-side sensor is a common cause.
- Book a service call.
Frequently asked questions
How many thermistors does a non-condensing Takagi have?
Fewer than a condensing one. This range has output and inlet thermistors, plus a mixing thermistor on the T-D2. There is no exhaust thermistor at all — that is a condensing-model part, and so is its code 341.
Code 311 on other Takagi series
Other Takagi series report code 311 under the same fault name, but each manual is transcribed separately and they do not read alike:
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: