High Lockout
A3317 on Worcester Bosch GB162

Your boiler has detected an electrical fault with the sensor that monitors exhaust gases, causing the system to shut down for safety.

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

Short circuit in the flue gas temperature sensor contacts

What causes this fault?

This fault occurs when the electrical connection for the sensor that monitors exhaust temperatures becomes damaged or fails. The most common reasons are water ingress from heavy rain or moisture in the flue damaging the sensor's contacts, or the wiring harness becoming brittle and failing due to the high heat inside the boiler casing.

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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