BoilerFaultCodesGlow-worm F49 Fault Code
The Glow-worm F49 fault code means: your boiler has lost communication with its external controls like your thermostat because there is an electrical problem with the wiring connecting them.. It appears on 6 Glow-worm models in our database.
Technical description: eBUS low voltage fault (short circuit)
What causes the Glow-worm F49 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 fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Glow-worm models that show the F49 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F49 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026