BoilerFaultCodesYour boiler has detected that a sensor monitoring the temperature of the water returning to the unit is giving an incorrect reading or has failed, causing the system to stop working as a safety precaution.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The heating return thermistor is too resistant.
What causes this fault?
This fault occurs when the internal control board receives a signal from the return water sensor that is outside of the expected range, suggesting the component is broken or disconnected. The most common reason is that the sensor's internal resistance has degraded over time, though it can also be caused by loose wiring or corrosion on the sensor pins. Because the boiler can no longer accurately monitor the temperature of the water coming back from your radiators, it shuts down to prevent overheating.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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