High Lockout
F49 on Glow-worm Ultracom 2 HXI

Your boiler has lost communication with its external controls like your thermostat because there is an electrical problem with the wiring connecting them.

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 low voltage fault (short circuit)

What causes this fault?

This fault occurs when the low-voltage communication line between your boiler and thermostat is interrupted, usually by a short circuit. The most common cause is a loose wire at a connection point or moisture getting into the external control box. In some cases, it can be triggered by a fault within the boiler's internal computer board failing to process the signal.

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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Related fault codes

F49View →F61View →F62View →

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