High Lockout
H.....4...... on Ideal Esprit HE

Your boiler has detected that a safety sensor in the exhaust pipe is reporting an incorrect temperature reading or has developed a fault.

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

FLUE THERMISTOR ERROR

What causes this fault?

This fault occurs when the sensor responsible for monitoring the temperature of the exhaust gases sends an illogical reading to the boiler's internal computer. It often happens because the sensor has physically degraded, developed a loose wiring connection, or the boiler is running too hot due to an internal blockage or heat exchanger issue. To ensure safety, the boiler shuts down to prevent any risk of the plastic flue components melting or overheating.

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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