High Lockout
L4 on Ideal Logic Combi C24 C30 C35

Your boiler has detected a problem with the internal temperature sensor that monitors the water leaving the unit, causing it to shut down as a safety precaution.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Flow Thermistor Fault

What causes this fault?

This fault occurs when the sensor responsible for measuring the heat of the water leaving your boiler fails to send a correct signal to the main control board. The most common reason is that the sensor has physically degraded or developed an electrical short, but it can also be caused by loose wiring or a glitch in the boiler's internal computer.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

L1View →L2View →F2View →

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