BoilerFaultCodesGrant 18 Fault Code
The Grant 18 fault code means: your boiler is not receiving enough fresh air to operate safely and efficiently, which usually means the external air intake or flue vent is blocked or obstructed.. It appears on 6 Grant models in our database.
Technical description: Vent A (in²)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Grant models that show the 18 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Grant 18 fault code information on this page is sourced and cross-checked against the official Grant service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026