BoilerFaultCodesYour boiler has detected an issue with the sensor that monitors hot water temperature, meaning it cannot safely heat water for your taps.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Domestic hot water thermistor fault
What causes this fault?
This fault occurs when the internal sensor responsible for measuring the temperature of your tap water fails or sends an incorrect signal to the main control board. The most common reason is that the sensor has physically degraded over time or developed a short circuit, preventing the boiler from knowing how hot the water is. In some cases, the issue may simply be loose or damaged wiring between the sensor and the boiler's computer.
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 F4 — no call-out fees, no surprises.
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