High
L4 or F4 on Ideal Compact HE

Your boiler has sensed a temperature sensor issue or a flow problem, causing it to shut down for safety to prevent overheating.

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

Control / no flow thermistor fault

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 →F1View →F2View →

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