High Lockout
FA9 on Glow-worm Energy Heat

Your boiler's internal communication system has lost power, meaning the different components cannot talk to each other to start the heating process.

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

eBUS fault – voltage too low

What causes this fault?

This fault occurs when the internal communication line, which allows the display and controls to talk to the main brain of the boiler, loses electrical power. The most common reason is a short circuit in the wiring or a failing printed circuit board that is no longer able to distribute the correct voltage. It can also be triggered if an external smart thermostat or controller draws too much power from the system.

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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