Takagi Water Heater Error Code 31: How to Fix It

Q: What does error code 31 mean on a Takagi tankless water heater?

Error code 31 on a Takagi water heater indicates a fault with the inlet thermistor — the sensor that monitors the temperature of incoming cold water. The unit shuts down to prevent unsafe operation when this sensor reads an abnormal or out-of-range value.

Q: Can I reset a Takagi error code 31 without fixing anything?

You can try a power cycle reset by turning off the breaker for 30 seconds and restarting the unit. This clears temporary glitches. However, if the underlying thermistor is faulty, the code will return. A reset alone is not a permanent fix.

Q: How much does it cost to replace a Takagi inlet thermistor?

The inlet thermistor part itself typically costs between $15 and $50 depending on your model. If you hire a plumber or technician for the repair, expect to add $75 to $150 or more in labor costs, making the total repair roughly $90 to $200.

Q: Will error code 31 prevent my Takagi from producing any hot water?

Yes, in most cases error code 31 will cause the Takagi heater to shut down completely and stop producing hot water as a safety measure. The heater will not operate normally until the thermistor fault is resolved and the error is cleared.

Q: How do I find the model number on my Takagi water heater?

The model number is printed on the rating label or data plate, which is typically located on the front face or side of the unit. You will need this model number to source the correct replacement inlet thermistor for your specific heater.

Abstract

Error code 31 on a Takagi tankless water heater indicates a fault with the inlet thermistor — the sensor that measures the temperature of cold water entering the unit. When this sensor fails or reads an out-of-range temperature, the heater shuts down as a safety precaution to prevent damage or dangerous operation. In many cases this is caused by a faulty thermistor, loose wiring, or a blocked water flow affecting the sensor reading.