Takagi tankless water heaters utilize digital error codes displayed on the remote controller or diagnostic flashing LED lights on the computer board to signal operational faults. Common codes include Code 111 (or 11), which indicates an ignition failure usually caused by closed gas valves, inadequate gas pressure, or dirty flame sensors. Code 991 (or 99) warns of abnormal or imperfect combustion, typically triggered by blocked intake/exhaust venting or incorrect fuel conversion settings. Code 711 points to a tripped high-limit safety switch or compromised thermal fuse due to overheating, while Code 311 indicates a faulty outlet thermistor measuring incorrect water temperatures.
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