BoilerFaultCodesThe boiler has detected that two internal temperature sensors have been swapped or are reading incorrectly, preventing the system from heating up safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: S1 and S2 interchanged
What causes this fault?
This fault occurs when the boiler's control board detects that the temperature readings for the water leaving the boiler and the water returning to it have been swapped. It is usually caused by a physical wiring error during a repair or a internal sensor failure where one part begins sending incorrect data to the system. Because the boiler cannot accurately track how heat is moving through the heat exchanger, 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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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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