BoilerFaultCodesYour boiler has detected a problem with the sensor that monitors the temperature of the water leaving the unit, causing it to shut down to prevent overheating.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Heating flow thermistor fault
What causes this fault?
This fault occurs when the internal sensor responsible for tracking the temperature of the water sent to your radiators fails or provides an illogical reading. The most common reason is that the sensor has physically degraded or developed an electrical short, meaning the boiler can no longer verify if it is operating at a safe temperature. In some cases, loose or damaged wiring between this sensor and the main control box can also trigger the error.
This fault is slightly more common in winter when the boiler is running at higher temperatures for longer periods, which places more thermal stress on the electrical components.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like F2 — no call-out fees, no surprises.
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