BoilerFaultCodesYour boiler has detected that a temperature sensor is not communicating correctly, meaning the system cannot tell how hot the water is and has stopped working for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Control / No flow thermistor
What causes this fault?
This fault occurs when the boiler's internal computer loses contact with the sensor that monitors the temperature of the water leaving the unit. The most common reason is that the sensor has either degraded due to constant heat cycles or the electrical connection between the sensor and the main control board has become faulty.
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 F4 — 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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