Takagi Water Heater Error Code 34: How to Fix It

Q: What does error code 34 mean on a Takagi tankless water heater?

Error code 34 on a Takagi tankless water heater means the control board has detected a short circuit in the flue thermistor — the sensor that monitors the temperature of exhaust gases leaving the unit. This causes the heater to shut down as a safety precaution.

Q: Can I reset a Takagi error code 34 without fixing anything?

You can attempt a reset, and occasionally a temporary power fluctuation can cause a one-time false trigger. However, if error code 34 returns after a reset, there is a real fault — either a failed thermistor, damaged wiring, or a flue blockage — that must be repaired before the unit will operate reliably and safely.

Q: How much does it cost to fix a Takagi error code 34?

A replacement flue thermistor typically costs between $20 and $60 for the part depending on the model. If you hire a technician, expect to pay $100-$250 for labor in addition to parts. If the control board is damaged and requires replacement, costs can rise to $300-$600 or more.

Q: Is it safe to use my Takagi water heater with error code 34 showing?

No. When error code 34 is active, the unit should shut itself down automatically. If for some reason it continues to run, the heater cannot properly monitor flue exhaust temperatures, creating a risk of overheating, flue damage, or in worst-case scenarios, a hazardous situation with exhaust gases. Do not bypass or ignore this error.

Q: How do I find the flue thermistor on my Takagi water heater?

After removing the front access panel with a Phillips screwdriver, look near the top of the unit at the exhaust flue outlet or heat exchanger exhaust port. The flue thermistor is a small sensor — often cylindrical or bullet-shaped — with two wires attached, mounted directly on or very close to the flue collar where hot exhaust gases exit the heat exchanger.

Abstract

Takagi error code 34 indicates that the flue thermistor — the temperature sensor that monitors the exhaust gases leaving your tankless water heater — has detected a short circuit in its wiring or sensor element. This can cause the unit to shut down as a safety measure to prevent overheating or flue damage. While this is a medium-severity issue, it should be addressed promptly because a faulty flue thermistor means your heater cannot properly monitor dangerous exhaust temperatures.