BoilerFaultCodes.com
51 High Lockout

Your boiler is unable to provide hot water because of a faulty internal sensor that has stopped communicating correctly.

Call an engineer soon

Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: No DHW heating - Cylinder temperature sensor 2/outlet sensor shorted out

What causes this fault?

This fault occurs when the internal electronic probe responsible for monitoring the hot water temperature develops an electrical short circuit. The boiler’s control board can no longer read the water temperature safely, so it disables the hot water function to prevent overheating. This is typically caused by natural wear and tear of the sensor or moisture ingress damaging the electrical connections over time.

Typical repair cost £120-£210 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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