High
S.42 on Glow-worm 30cxi

Your boiler has detected a communication error with an external add-on control, such as an internet gateway or smart thermostat controller, which is preventing the boiler from firing up.

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.

What the manual says

Manufacturer manual

Accesory Module is blocking burner operation

From this model's manual
Verified against the Glow Worm Glow Worm 30cxi installation & service manual, page 52.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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

S.41View →S.43View →

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