High Lockout
4Y on Ideal Maximiser SE

Your boiler has lost its connection to the internal thermometer that monitors water temperature, meaning it cannot safely heat your home or water.

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

Supply sensor not connected.

What causes this fault?

This fault occurs when the boiler's main computer loses communication with the temperature sensor attached to the internal pipework. It is usually caused by the sensor failing due to age, or a loose connection or damaged wire preventing the signal from reaching the control board.

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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