BoilerFaultCodesYour boiler has detected a problem with a temperature sensor on the main internal heat exchanger, causing it to shut down for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Lockout Burner Mains - Automatic Casting Thermistor Fault
What causes this fault?
This fault occur when the sensor responsible for monitoring the temperature of the boiler's main heat exchanger sends an incorrect or out-of-range signal to the control board. The most common cause is a physical failure of the thermistor itself due to age, or potentially a loose connection in the wiring that prevents the boiler from safely monitoring internal heat levels.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like Casting Thermistor Fault — no call-out fees, no surprises.
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