BoilerFaultCodesTechnical description
Appears if a problem exists with the primary thermistor.
What causes this fault?
This fault occurs when the boiler's internal thermometer, known as a thermistor, stops sending a reliable reading to the main control board. The most common reason is that the sensor has physically failed due to age or internal wear, though loose or damaged wiring between the sensor and the circuit board can also break the signal.
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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