High Lockout
432 on Ideal Response SE

Your boiler has detected a faulty internal temperature sensor that is preventing the system from heating up safely.

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

NTC 2 short circuit

What causes this fault?

This fault occurs when the boiler's internal temperature sensor develops an electrical short circuit, preventing it from reading the water temperature correctly. The most common reason is that the sensor's internal components have physically failed due to age or heat stress, though it can also be caused by water damage to the electrical connector.

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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