BoilerFaultCodesYour boiler has stopped working because it cannot detect any water flowing through the system, meaning it cannot safely heat your home or water.
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 fault
What causes this fault?
This fault occurs when the boiler's internal flow sensor fails to detect water movement when the pump is running. The most common reasons are a mechanical failure of the sensor itself, a blockage preventing water circulation, or a communication issue between the sensor and 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
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A boiler cover plan would cover faults like FO30 — 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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