High Lockout
CH light on PCB 40 flashing on Ideal Response

Your boiler has detected a communication problem or a fault with the sensor that controls your central heating temperature.

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

Check the CH sensor and panel control and/or the wires connecting them to the PCB.

What causes this fault?

This fault occurs when the boiler's main computer loses touch with the sensor that monitors your heating water temperature. It usually happens because the sensor has failed internally or the electrical wires connecting it to the control board have become loose or damaged. Without this vital temperature data, the boiler shuts down as a safety precaution to prevent overheating.

This fault often appears when the heating is first turned on in autumn, as the sudden change in temperature can cause aging electrical sensors to fail.

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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