391 🟡 Repair Required
Takagi Error Code 391: Exhaust Temp Sensor
⚠️ The tankless water heater has shut down due to a potential issue with the exhaust temperature sensor. Hot water is unavailable until the problem is resolved.
How to Fix Takagi Code 391
- Step 1: Check the exhaust vent outside the house for any visible obstructions like leaves, snow, or debris. Clear any blockages.
- Step 2: Reset the unit by turning off the power at the breaker for a few minutes, then turning it back on. See if the error code clears.
- Step 3: If the error code persists after checking the vent and resetting the unit, contact a qualified HVAC technician to diagnose and repair the problem.
What Does Takagi Error Code 391 Mean?
The Takagi error code 391 indicates a problem with the exhaust temperature sensor. This sensor monitors the temperature of the exhaust gases leaving the unit. If the temperature exceeds a set limit or the sensor malfunctions, the unit will shut down as a safety precaution. This is important because excessively high exhaust temperatures can indicate combustion problems, venting issues, or other malfunctions that could damage the unit or, in very rare cases, pose a safety risk. The unit locks out to prevent further operation until the issue is addressed. The sensor is designed to protect the unit from overheating and to ensure proper combustion.
Common Causes of Takagi Code 391
- Faulty exhaust temperature sensor
- Obstructed or blocked venting system
- Combustion issues leading to high exhaust temperatures
- Wiring issues or loose connections to the exhaust temperature sensor
- Scale buildup on the heat exchanger causing overheating
Applicable Takagi Models
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Find a Licensed Tech Near You →Replacement Parts for Takagi HVAC System Code 391
Exhaust Temperature Sensor OEM: TK190012
Combustion Fan Motor
Gas Valve