BoilerFaultCodesYour boiler has lost communication with one of its internal heat sensors, meaning it cannot monitor temperatures accurately to operate safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Sensor S3 lead break
What causes this fault?
This fault occurs when the boiler's control board loses its electrical connection to a specific internal temperature sensor. The most common cause is a failure of the sensor itself or loose, damaged wiring that prevents the boiler from safely monitoring the water temperature. Without this data, the system 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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A boiler cover plan would cover faults like 9B — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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