BoilerFaultCodesYour boiler has switched itself off because the internal temperature sensors are giving conflicting or unusual readings, meaning it cannot safely regulate the heat.
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 Flow Thermistor Fault (Thermistors reading outside of limits or difference between readings outside of limits)
What causes this fault?
This fault occurs when the sensors responsible for monitoring the temperature of the water leaving the boiler fail to report consistent data. The most common reason is that the internal components of the sensor have degraded over time, though it can also be caused by loose wiring or a communication error within the main control board.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like Flow Thermistor Fault — no call-out fees, no surprises.
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