BoilerFaultCodesYour boiler's temperature control dial is no longer reading the heat correctly, causing the system to shut down or behave inconsistently 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: Thermostat out of calibration or faulty
What causes this fault?
This fault occurs when the mechanical sensing bulb inside the thermostat fails to accurately gauge the temperature of the water. Over time, the internal components can wear out or lose calibration, meaning the boiler can no longer safely determine when to turn the burner off. This leads to the system shutting itself down to prevent the water from reaching dangerously high temperatures.
This issue often becomes apparent in autumn when the heating is first switched back on after summer, as the moving parts within the thermostat can seize up through lack of use.
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 C(4) — no call-out fees, no surprises.
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