High Lockout
4U on Ideal Maximiser SE

Your boiler has stopped working because an internal temperature sensor has developed an electrical fault and can no longer read the heat levels correctly.

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 short-circuited.

What causes this fault?

This fault occurs when the electrical resistance in the main temperature sensor drops to an abnormal level, suggesting a short circuit. The most common reason is that the sensor's internal components have perished over time, or moisture has compromised the electrical connections. Because the boiler can no longer safely monitor how hot the water is getting, it shuts down as a safety precaution.

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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