BoilerFaultCodesTechnical description
Flue thermistor fault or heat exchanger needs cleaning
What causes this fault?
This fault occurs when the internal safety sensors detect that the exhaust gases are becoming too hot, which is often a sign that heat isn't being transferred efficiently to your water. The most common reason is a buildup of debris and carbon deposits inside the main heat exchanger, which restricts airflow and causes the unit to overheat. In some cases, the sensor itself may have simply failed or developed a loose connection, sending an incorrect reading to the control board.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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