High Lockout
HW light on PCB 40 flashing on Ideal Response

Your boiler has detected a fault with the temperature sensor that controls your hot water, meaning it cannot accurately measure how hot the water is.

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 HW sensor/lead. Sensor may have failed 'low resistance'.

What causes this fault?

This fault occurs when the boiler's internal computer receives an incorrect electrical signal from the hot water temperature sensor. It usually means the sensor has developed a short circuit or the wiring connecting it to the main control board has become damaged or loose. Because the boiler no longer knows how hot the water is, it shuts down as a safety precaution to prevent 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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