300 mm Emergency

Malvern 300 mm Fault Code

Also written as 300MM — same fault.

The Malvern 300 mm fault code means: your boiler has detected that it is positioned too close to a window or ventilation point, which poses a safety risk regarding airflow and flue gases.. It appears on 1 Malvern model in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: Below window or vent

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Malvern models that show the 300 mm fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Malvern 300 mm fault code information on this page is sourced and cross-checked against the official Malvern service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026