BoilerFaultCodesYour boiler's main internal temperature sensor has stopped working correctly, which means the system cannot safely monitor heat levels and has shut down as a precaution.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: S1 sensor defect. Replace S1.
What causes this fault?
This fault occurs when the boiler's main flow temperature sensor fails to send a consistent electrical signal to the control board. The most common reasons are the internal components of the sensor wearing out over time or a loose connection in the wiring harness. Because the boiler can no longer monitor how hot the water is getting, it shuts down immediately 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 2 — 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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