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
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: